refactor: remove legacy PWA service worker and update related assets

[chenyme]

Summary

Retire the PWA caching Service Worker while preserving the Web App Manifest, installable experience, and PWA icons.

Replace the existing worker with a migration-only tombstone that clears legacy deeix-chat-* caches and unregisters itself. Separate the temporary migration code from shared UI components and remove Service Worker coupling from Docker, version synchronization, and PWA asset generation.

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

• cd frontend && pnpm lint
• node frontend/scripts/sync-pwa-assets.mjs
• node scripts/sync-version.mjs frontend --check
• git diff --check
• Build not run per request.

Screenshots, API examples, or logs

Not applicable. This change has no visible UI changes.

Configuration, migration, and compatibility notes

Existing installations may already have /sw.js registered. This release retains /sw.js as a migration-only worker that:

• Deletes caches prefixed with deeix-chat-
• Takes control of existing clients without intercepting requests
• Unregisters itself after activation

New clients do not register a Service Worker. The Web App Manifest and PWA icons remain available.

The migration worker and its client-side migration entry should remain available for the supported upgrade window so self-hosted installations can skip intermediate releases safely.

No API, database, environment variable, or public URL changes are required.

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 browser cache cleanup and Service Worker lifecycle behavior.

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.