feat(plugins): show installed state in marketplace and search installed extensions

Marketplace cards now reflect whether an extension is already installed in
the current workspace, and the installed-extension list gains a search box.

Backend (stream install progress):
- _read_httpx_response_limited gains an optional task_context: it publishes
  download_total from Content-Length before the first chunk and updates
  download_current / download_speed per chunk. The marketplace download path
  previously had no progress reporting; it now matches the GitHub path.
- _marketplace_get forwards task_context to that helper.
- install_plugin resets the per-install counters so re-installing the same
  plugin cannot inherit stale metadata, and reports human-readable stages:
  preparing -> downloading -> inspecting -> storing -> installing
  dependencies -> launching -> waiting for plugin to become ready.

Frontend (installed state):
- New marketplace-installed helper normalises the sidebar identities
  (plugin: author/name, mcp: author__name, skill: bare name) into one
  type:author/name index and resolves a card's installed state from it.
  useMarketplaceInstalledIndex memoises on the sidebar lists, so a finished
  install (which refreshes the sidebar) re-evaluates the cards automatically.
- PluginMarketCardVO carries installed / hasUpdate. An installed extension
  turns its download affordance into a hollow green ring with a green check
  in place, instead of adding a separate badge; the count slot switches to
  the installed label. Cards with an available update use amber.
- PluginMarketComponent derives the annotated list and shares the index with
  RecommendationLists.

Frontend (install task UI):
- mapActionToStage matches the new connector stage strings. The pre-download
  stages are checked before the generic "install" match, because
  "preparing plugin install" also contains "install".
- Stage progress ranges are non-overlapping; overall progress interpolates on
  real byte counts while downloading and drifts monotonically elsewhere,
  capped at 99%.
- The progress dialog and task queue expose the launching stage.

Frontend (installed list search):
- The installed list had no search at all. A query box in the page header
  filters by label / name / author / description, case-insensitively, applied
  before grouping so grouped and flat views both honour it.
- Search misses and an empty list now show distinct empty states, with a
  clear action on a search miss.
- AsyncTask entity gains the optional created_at field.

i18n: new marketplace / install / search strings across all 8 locales.

Verified: ruff format + check, tsc --noEmit, prettier --check, eslint
(0 errors), and 89/89 frontend unit tests.

src/langbot/pkg/plugin/connector.py

@@ -87,8 +87,10 @@ async def _read_httpx_response_limited(
     response: httpx.Response,
     *,
     max_bytes: int,
+    task_context: taskmgr.TaskContext | None = None,
 ) -> bytes:
     content_length = response.headers.get('content-length')
+    declared_size: int | None = None
     if content_length is not None:
         try:
             declared_size = int(content_length)
@@ -97,11 +99,25 @@ async def _read_httpx_response_limited(
         if declared_size is not None and declared_size > max_bytes:
             raise ValueError(f'Remote response exceeds the {max_bytes}-byte limit')
 
+    if task_context is not None and declared_size is not None:
+        # Publish the advertised size up-front so the UI can render a
+        # determinate bar even before the first chunk arrives.
+        task_context.metadata['download_total'] = declared_size
+
+    start_time = time.time()
     body = bytearray()
     async for chunk in response.aiter_bytes(chunk_size=64 * 1024):
         body.extend(chunk)
         if len(body) > max_bytes:
             raise ValueError(f'Remote response exceeds the {max_bytes}-byte limit')
+        if task_context is not None:
+            elapsed = time.time() - start_time
+            task_context.metadata.update(
+                {
+                    'download_current': len(body),
+                    'download_speed': len(body) / elapsed if elapsed > 0 else 0,
+                }
+            )
     return bytes(body)
 
 
@@ -111,6 +127,7 @@ async def _marketplace_get(
     *,
     max_bytes: int,
     allow_not_found: bool = False,
+    task_context: taskmgr.TaskContext | None = None,
 ) -> tuple[int, bytes]:
     async with client.stream('GET', url) as response:
         if allow_not_found and response.status_code == 404:
@@ -119,6 +136,7 @@ async def _marketplace_get(
         return response.status_code, await _read_httpx_response_limited(
             response,
             max_bytes=max_bytes,
+            task_context=task_context,
         )
 
 
@@ -1680,6 +1698,7 @@ class PluginRuntimeConnector(ManagedRuntimeConnector):
                 client,
                 f'{space_url}/api/v1/marketplace/plugins/download/{plugin_author}/{plugin_name}/{latest_version}',
                 max_bytes=_MARKETPLACE_PLUGIN_DOWNLOAD_MAX_BYTES,
+                task_context=task_context,
             )
             return plugin_package, latest_version
 
@@ -1695,7 +1714,21 @@ class PluginRuntimeConnector(ManagedRuntimeConnector):
         plugin_name = str(install_info.get('plugin_name') or '')
         file_bytes: bytes | None
 
+        if task_context is not None:
+            # Reset the per-install counters so re-installing the same plugin
+            # cannot inherit stale progress metadata from a previous task.
+            task_context.set_current_action('preparing plugin install')
+            task_context.metadata.update(
+                {
+                    'download_total': 0,
+                    'download_current': 0,
+                    'download_speed': 0,
+                }
+            )
+
         if install_source == PluginInstallSource.MARKETPLACE:
+            if task_context is not None:
+                task_context.set_current_action('downloading plugin package')
             file_bytes, version = await self._download_marketplace_package(
                 execution_context,
                 plugin_author,
@@ -1719,6 +1752,8 @@ class PluginRuntimeConnector(ManagedRuntimeConnector):
         else:
             raise ValueError(f'Unsupported plugin install source: {install_source.value}')
 
+        if task_context is not None:
+            task_context.set_current_action('inspecting plugin package')
         manifest_author, manifest_name = self._inspect_plugin_package(file_bytes, task_context)
         if not manifest_author or not manifest_name:
             raise ValueError('Plugin package manifest identity is missing')
@@ -1730,8 +1765,12 @@ class PluginRuntimeConnector(ManagedRuntimeConnector):
         if task_context is not None:
             task_context.metadata['plugin_name'] = f'{plugin_author}/{plugin_name}'
 
+        if task_context is not None:
+            task_context.set_current_action('storing plugin package')
         artifact_digest = hashlib.sha256(file_bytes).hexdigest()
         await self._store_artifact_package(execution_context, artifact_digest, file_bytes)
+        if task_context is not None:
+            task_context.set_current_action('installing plugin dependencies')
         try:
             binding, previous_digest, previous_was_durable = await self._persist_installation_package(
                 execution_context,
@@ -1749,6 +1788,8 @@ class PluginRuntimeConnector(ManagedRuntimeConnector):
             plugin_author=plugin_author,
             plugin_name=plugin_name,
         )
+        if task_context is not None:
+            task_context.set_current_action('launching plugin')
         await self._apply_desired_state(
             PluginInstallationDesiredState(binding=binding, enabled=True),
             artifact_package=file_bytes,
@@ -1766,6 +1807,8 @@ class PluginRuntimeConnector(ManagedRuntimeConnector):
                         pass
             except Exception as exc:
                 self.ap.logger.debug(f'Legacy OSS plugin cleanup skipped: {exc}')
+        if task_context is not None:
+            task_context.set_current_action('waiting for plugin to become ready')
         await self._wait_for_installed_plugin_ready(plugin_author, plugin_name, task_context)
 
     async def upgrade_plugin(