* fix: use full IP for userId to prevent quota collision
- Remove .slice(0, 8) from base64 encoded IP
- Each IP now has unique userId (no /16 collision)
- Affects: quota tracking, Langfuse tracing
* refactor: extract getUserIdFromRequest to shared utility
- Create lib/user-id.ts with shared function
- Fix misleading 'privacy' comment (base64 is not privacy)
- Remove duplicate code from chat and log-feedback routes
- Add Biome as formatter and linter (replaces Prettier)
- Configure Husky + lint-staged for pre-commit hooks
- Add VS Code settings for format on save
- Ignore components/ui/ (shadcn generated code)
- Remove semicolons, use 4-space indent
- Reformat all files to new style
- Add Zod schema validation for log-feedback and log-save endpoints
- Create singleton LangfuseClient to avoid per-request instantiation
- Simplify log-save to only flag trace (no XML content sent)
- Use generic error messages to prevent info leakage
- Update log-feedback API to find existing chat trace by sessionId and attach score to it
- Update log-save API to create span on existing chat trace instead of standalone trace
- Add thumbs up/down feedback buttons on assistant messages
- Add message regeneration and edit functionality
- Add save dialog with format selection (drawio, png, svg)
- Pass sessionId through components for Langfuse linking
