Add local development build workflow

- Add Makefile targets: install, type-check, lint, build-local
- Add type-check script to backend/package.json
- Create backend/.gitignore for build artifacts

Enables quick TypeScript error detection without Docker rebuilds.

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

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

backend/package.json

@@ -14,7 +14,8 @@
     "migrate:all": "ts-node src/_system/migrations/run-all.ts",
     "migrate:feature": "ts-node src/_system/migrations/run-feature.ts",
     "schema:generate": "ts-node src/_system/schema/generate.ts",
-    "lint": "eslint src"
+    "lint": "eslint src",
+    "type-check": "tsc --noEmit"
   },
   "dependencies": {
     "pg": "^8.13.1",