feat: add animal tagging projection and service

Implement AnimalTagged and AnimalTagEnded event handling:
- Add migration for tag_suggestions table
- Create TagProjection for tag intervals and suggestions
- Update EventAnimalsProjection to handle tag events
- Add add_tag() and end_tag() to AnimalService

Key behaviors:
- No-op idempotence (adding active tag or ending inactive tag)
- Updates live_animals_by_location.tags JSON array
- Tracks tag usage statistics in tag_suggestions

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

migrations/0005-tag-suggestions.sql

@@ -0,0 +1,15 @@
+-- ABOUTME: Migration to create tag_suggestions table.
+-- ABOUTME: Tracks tag usage for autocomplete in the UI.
+
+-- Tag suggestions for autocomplete
+-- Updated synchronously during tagging operations
+CREATE TABLE tag_suggestions (
+    tag TEXT PRIMARY KEY,
+    total_assignments INTEGER NOT NULL DEFAULT 0,
+    active_animals INTEGER NOT NULL DEFAULT 0,
+    last_used_utc INTEGER,
+    updated_at_utc INTEGER NOT NULL
+);
+
+-- Index for sorting by popularity
+CREATE INDEX idx_tag_suggestions_popularity ON tag_suggestions(active_animals DESC, total_assignments DESC);