feat(mcp): simplify external MCP server config to local/remote modes

Replace the three-way transport choice (stdio / sse / httpstream) for
connecting LangBot to external MCP servers with two modes: local (stdio)
and remote. Remote servers only require a URL; the runtime auto-detects
the transport (tries Streamable HTTP, falls back to SSE).

- provider/tools/loaders/mcp.py: add _init_remote_server() with
  Streamable-HTTP-then-SSE probing; dispatch 'remote' lifecycle, keep
  legacy sse/http branches for back-compat
- plugin/connector.py: normalize legacy http/sse marketplace modes to
  'remote' on Space install, preserving connection params
- entity/persistence/mcp.py: document mode as stdio, remote (legacy: sse, http)
- alembic 0006: idempotent data migration mapping existing sse/http rows
  to remote (downgrade maps back to http)
- api/http/service/mcp.py: stash runtime_info (status + tool list) into
  test task metadata before tearing down the temp session
- web: collapse mode dropdown to local/remote, remote renders URL+timeout
  only, edit auto-maps legacy sse/http to remote; show tools after test in
  create mode from task metadata; remove dead plugins/mcp-server/ tree
- i18n: local/remote labels + mode/url hints across 8 locales

web/src/app/home/plugins/components/plugin-installed/ExtensionCardVO.ts

@@ -17,7 +17,7 @@ export interface IExtensionCardVO {
   hasUpdate?: boolean;
   runtimeStatus?: 'connecting' | 'connected' | 'error' | 'disabled';
   tools?: number;
-  mode?: 'stdio' | 'sse' | 'http';
+  mode?: 'stdio' | 'sse' | 'http' | 'remote';
 }
 
 export class ExtensionCardVO implements IExtensionCardVO {
@@ -37,7 +37,7 @@ export class ExtensionCardVO implements IExtensionCardVO {
   hasUpdate?: boolean;
   runtimeStatus?: 'connecting' | 'connected' | 'error' | 'disabled';
   tools?: number;
-  mode?: 'stdio' | 'sse' | 'http';
+  mode?: 'stdio' | 'sse' | 'http' | 'remote';
 
   constructor(prop: IExtensionCardVO) {
     this.id = prop.id;