feat: support manual file vectorization

[chenyme]

Summary

Adds manual vectorization for eligible files when automatic vectorization is disabled or a previous indexing attempt needs to be retried.

• Support single-file and batch vectorization with a 100-file limit.
• Add vectorization actions to the Files page and knowledge base details.
• Preserve user and admin file ownership boundaries.
• Introduce a dedicated recoverable embedding queue with bounded concurrency retry handling and terminal failure states.
• Expose queued processing and vectorization capability states through the API.
• Avoid automatic extraction and OCR runtime probes when opening or saving file settings.
• Update Swagger and generated TypeScript API contracts.

Closes #688.

Change type

• Bug fix
• Feature
• Documentation
• Refactor
• Configuration / deployment
• Security hardening
• Other

Affected areas

• Frontend / UI
• Backend / API
• Authentication / authorization
• Conversations / streaming
• Files / RAG / extraction
• Model routing / providers
• MCP / tools
• Billing / payments
• Admin console
• Deployment / Docker / configuration
• Documentation

Verification

• go vet ./...
• go test ./...
• go test -race ./internal/application/embedding ./internal/application/processing ./internal/infra/cache/memory ./internal/infra/cache/redis
• pnpm check
• pnpm build
• pnpm api:check
• git diff --check
• Not run; reason:

Screenshots, API examples, or logs

New endpoints:

• POST /api/v1/files/embeddings
• POST /api/v1/admin/knowledge-bases/files/embeddings

Request body:

{
  "fileIDs": ["file-id"]
}

Configuration, migration, and compatibility notes

• No database migration is required.
• No configuration or deployment changes are required.
• Existing automatic vectorization behavior remains unchanged.
• Manual vectorization works independently of the automatic upload trigger.
• API responses now include vectorization capability and queued-state information.
• Swagger and generated TypeScript contracts are updated.
• The change is backward compatible.

Documentation

• Documentation is not needed for this change.
• Documentation was updated.
• Documentation still needs to be updated.

Security and privacy

• No secrets, tokens, credentials, local config, or personal data are included.
• User data access remains scoped by authenticated user context unless an admin-only path explicitly requires broader access.
• Security-sensitive behavior was reviewed, including authentication, authorization, provider routing, file processing, billing, and admin APIs where relevant.

Checklist

• I searched existing issues and pull requests.
• Changes are focused and do not include unrelated refactors.
• Tests or static verification were run where practical.
• User-facing behavior, deployment steps, API contracts, or configuration changes are documented.
• Generated artifacts are included only when this project explicitly requires them.
• Caches, build output, .pyc files, .env files, and local storage data are not committed.