Feat/dbm20 rag (#2037)

* feat(rag): add knowledge base migration from v4.9.0 to plugin architecture

Rewrite dbm020 to backup old knowledge_bases data and preserve
external_knowledge_bases table. Add migration API endpoints and
frontend dialog so users can opt-in to auto-install LangRAG plugin
and restore their knowledge bases with original UUIDs preserved.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix(rag): query marketplace for actual plugin version instead of 'latest'

The marketplace API does not support 'latest' as a version string.
Fetch the plugin info first to get latest_version, then use that
concrete version for installation.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* feat(rag): add data-only migration option and fix dialog width

Add option to migrate knowledge base data without auto-installing
the LangRAG plugin (for offline/intranet environments). Also
narrow the migration dialog to match other confirmation dialogs.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* refactor: to red and no more

* fix lint

* fix ruff lint

* feat: add external migration

* fix: show

* feat: add external plugin auto download

* feat: update migration messages for knowledge base in multiple languages

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Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Junyan Qin <rockchinq@gmail.com>

src/langbot/pkg/utils/constants.py

@@ -2,7 +2,7 @@ import langbot
 
 semantic_version = f'v{langbot.__version__}'
 
-required_database_version = 19
+required_database_version = 20
 """Tag the version of the database schema, used to check if the database needs to be migrated"""
 
 debug_mode = False