refactor: move supabase config to repo root, fix port and env setup

- Move supabase/ from packages/db/ to repo root for simpler CLI usage
- Use custom ports (553xx) to avoid conflicts with other local Supabase instances
- Add --env-mode=loose to turbo dev so root .env vars reach Next.js
- Remove hardcoded --port 3000 from next dev (reads PORT env var instead)
- Add .env.example with Supabase env var placeholders
- Add supabase local state dirs to .gitignore

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

supabase/migrations/20240216000003_create_view_increment_function.sql

@@ -0,0 +1,9 @@
+-- Function to atomically increment view count
+CREATE OR REPLACE FUNCTION increment_property_views(property_id TEXT)
+RETURNS void AS $$
+BEGIN
+  UPDATE properties
+  SET views = views + 1
+  WHERE id = property_id;
+END;
+$$ LANGUAGE plpgsql SECURITY DEFINER;