docs(04-01): complete tag schema and repository plan

Tasks completed: 2/2
- Add tags schema with case-insensitive unique index
- Create tagRepository with tag operations

SUMMARY: .planning/phases/04-tags/04-01-SUMMARY.md

.planning/phases/04-tags/04-01-SUMMARY.md

@@ -0,0 +1,99 @@
+---
+phase: 04-tags
+plan: 01
+subsystem: database
+tags: [drizzle, sqlite, many-to-many, tags, junction-table]
+
+# Dependency graph
+requires:
+  - phase: 01-foundation
+    provides: entries and images schema, repository pattern
+provides:
+  - tags table with case-insensitive unique constraint
+  - entry_tags junction table for many-to-many relationships
+  - tagRepository with findOrCreate, getAll, getById, getByEntryId, updateEntryTags
+  - lower() SQL helper function for case-insensitive queries
+affects: [04-02-tag-ui, 04-03-tag-filter, future-search]
+
+# Tech tracking
+tech-stack:
+  added: []
+  patterns:
+    - "Case-insensitive unique index using lower() SQL helper"
+    - "Junction table with composite primary key"
+    - "Atomic tag replacement via delete-then-insert"
+
+key-files:
+  created: []
+  modified:
+    - src/lib/server/db/schema.ts
+    - src/lib/server/db/repository.ts
+
+key-decisions:
+  - "Tags stored with original case but matched case-insensitively"
+  - "Entry tags replaced atomically (full replace, not incremental)"
+  - "Orphaned tags remain in database for autocomplete history"
+
+patterns-established:
+  - "lower() helper: Use for case-insensitive SQL comparisons"
+  - "Junction table: Composite PK with cascade deletes on both FKs"
+
+# Metrics
+duration: 2min
+completed: 2026-01-31
+---
+
+# Phase 4 Plan 1: Tag Schema & Repository Summary
+
+**Tags and entry_tags tables with case-insensitive uniqueness, cascade deletes, and tagRepository with atomic entry tag updates**
+
+## Performance
+
+- **Duration:** 2 min
+- **Started:** 2026-01-31T12:02:29Z
+- **Completed:** 2026-01-31T12:04:34Z
+- **Tasks:** 2
+- **Files modified:** 2
+
+## Accomplishments
+- Tags table with case-insensitive unique index on name using lower() helper
+- Entry_tags junction table with composite primary key and cascade deletes
+- TagRepository with findOrCreate, getAll, getById, getByEntryId, updateEntryTags methods
+- Database schema synced via drizzle-kit push
+
+## Task Commits
+
+Each task was committed atomically:
+
+1. **Task 1: Add tags schema with case-insensitive unique index** - `7dc63e6` (feat)
+2. **Task 2: Create tagRepository with tag operations** - `378d928` (feat)
+
+## Files Created/Modified
+- `src/lib/server/db/schema.ts` - Added tags table, entry_tags junction table, lower() helper, type exports
+- `src/lib/server/db/repository.ts` - Added TagRepository interface and SQLiteTagRepository implementation
+
+## Decisions Made
+- Store tags with original user-provided casing but match case-insensitively
+- Replace entry tags atomically: delete all existing, then insert new set
+- Keep orphaned tags in database (useful for autocomplete suggestions)
+
+## Deviations from Plan
+
+None - plan executed exactly as written.
+
+## Issues Encountered
+
+None
+
+## User Setup Required
+
+None - no external service configuration required.
+
+## Next Phase Readiness
+- Tag schema and repository ready for UI integration
+- Ready for plan 04-02 (tag input UI with autocomplete)
+- Ready for plan 04-03 (filter by tag)
+
+---
+*Phase: 04-tags*
+*Completed: 2026-01-31*