Fix schema drift: fresh installs were broken

- Create heat_cycles table in init.js (breeding.js used it but nothing created it)
- Add litters columns the routes actually use (breeding_date, whelping_date, puppy_count)
- Add health_records columns used by puppy logs (record_date, description)
- Puppy log insert now also sets NOT NULL test_date
- Migration 002 no-ops on a fresh DB instead of crashing on missing dogs table
- init.js honors DB_PATH and creates the data dir, so migrations and the app
  always target the same file

Verified: full heat-cycle/litter/puppy-log CRUD passes against a virgin database.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server/routes/litters.js

@@ -214,10 +214,11 @@ router.post('/:litterId/puppies/:puppyId/logs', (req, res) => {
       notes: notes || ''
     });
     
+    // test_date mirrors record_date: the column is NOT NULL on fresh schemas
     const result = db.prepare(`
-      INSERT INTO health_records (dog_id, record_type, record_date, description, vet_name)
-      VALUES (?, ?, ?, ?, ?)
-    `).run(puppyId, record_type || 'weight_log', record_date, description, null);
+      INSERT INTO health_records (dog_id, record_type, record_date, test_date, description, vet_name)
+      VALUES (?, ?, ?, ?, ?, ?)
+    `).run(puppyId, record_type || 'weight_log', record_date, record_date, description, null);
     
     const log = db.prepare('SELECT * FROM health_records WHERE id = ?').get(result.lastInsertRowid);
     res.status(201).json(log);