Add Other Purchases to budget page

- New other_purchases table (date, total, notes)
- /api/other CRUD endpoints
- Budget stats now include other costs in cost/egg and cost/dozen math
- Budget page: new Log Other Purchases form, stat cards for other costs,
  combined Purchase History table showing feed and other entries together

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/main.py

@@ -1,7 +1,7 @@
 from fastapi import FastAPI
 from fastapi.middleware.cors import CORSMiddleware
 
-from routers import eggs, flock, feed, stats
+from routers import eggs, flock, feed, stats, other
 
 app = FastAPI(title="Eggtracker API")
 
@@ -16,6 +16,7 @@ app.add_middleware(
 app.include_router(eggs.router)
 app.include_router(flock.router)
 app.include_router(feed.router)
+app.include_router(other.router)
 app.include_router(stats.router)