feat: implement user defaults persistence (Step 9.3)

Add user_defaults table and repository for persisting form defaults
across sessions. Feed and egg forms now load/save user preferences.

Changes:
- Add migration 0009-user-defaults.sql with table schema
- Add UserDefault model and UserDefaultsRepository
- Integrate defaults into feed route (location, feed_type, amount)
- Integrate defaults into egg route (location)
- Add repository unit tests and route integration tests

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

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

migrations/0009-user-defaults.sql

@@ -0,0 +1,17 @@
+-- ABOUTME: Migration for user_defaults table
+-- ABOUTME: Stores per-user form defaults (location, feed type, etc.) that persist across sessions
+
+CREATE TABLE user_defaults (
+  username TEXT NOT NULL REFERENCES users(username),
+  action TEXT NOT NULL CHECK(action IN ('collect_egg','feed_given')),
+  location_id TEXT,
+  species TEXT,
+  animal_filter TEXT,
+  feed_type_code TEXT,
+  amount_kg INTEGER,
+  bag_size_kg INTEGER,
+  updated_at_utc INTEGER NOT NULL,
+  PRIMARY KEY (username, action)
+);
+
+CREATE INDEX idx_user_defaults_username ON user_defaults(username);