feat: add project tags for organizing services

[cucumber-sp]

Summary

Implements Option B (Tags) from #3703 — project tagging system for organizing services at scale.

• Tag management page in Settings (create, edit, delete tags with custom colors, scoped per organization)
• Tag selector in project create/edit form with inline "Create Tag" action when no tags exist
• Tag filter on the project list with count badge and localStorage persistence
• Tag badges displayed on project cards for visual identification
• Database schema: tag and project_tag tables with Drizzle migration, organization scoping, and cascade deletes

Screenshots

Test plan

• Create tags with different colors in Settings > Tags
• Edit and delete existing tags
• Assign tags to projects via create/edit project form
• Verify tag badges appear on project cards
• Filter projects by tags (OR logic — shows projects matching any selected tag)
• Verify tag filter persists across page reloads (localStorage)
• Verify "Create Tag" button appears in empty tag dropdowns
• Verify tags are scoped per organization
• Verify cascade delete (deleting a tag removes it from all projects and clears filter)

Fixes #3703

Greptile Overview

Greptile Summary

Implements a comprehensive project tagging system with proper organization scoping, tag management UI, and filtering capabilities. The implementation includes database schema with cascade deletes, API endpoints with authorization checks, and React components for tag creation, assignment, and filtering with localStorage persistence.

Confidence Score: 5/5

• This PR is safe to merge with minimal risk
• The implementation demonstrates strong engineering practices with proper authorization checks, organization scoping, database constraints, and cascade deletes. The tag router includes comprehensive security validations, the frontend components handle edge cases well, and the localStorage-based filter persistence includes cleanup logic for deleted tags.
• No files require special attention

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