fix: code-driven OpenAPI docs — replace static JSON with swagger-jsdoc

BREAKING: OpenAPI spec is now generated from JSDoc annotations on route
handlers at startup, eliminating drift between code and documentation.

What was wrong:
- Static public/openapi.json was manually maintained and could drift
- Missing endpoints: signup, billing (checkout/success/webhook)
- Signup route was imported but never mounted (dead code)

What was fixed:
- Added swagger-jsdoc to generate OpenAPI spec from JSDoc on route files
- Every route handler now has @openapi JSDoc annotation as source of truth
- Spec served dynamically at GET /openapi.json (no static file)
- Deleted public/openapi.json
- Documented all missing endpoints (signup, billing x3)
- Mounted /v1/signup route
- All 9 screenshot params documented with types, ranges, defaults

package.json

@@ -18,13 +18,15 @@
     "pg": "^8.13.0",
     "pino": "^10.3.1",
     "puppeteer": "^24.0.0",
-    "stripe": "^17.0.0"
+    "stripe": "^17.0.0",
+    "swagger-jsdoc": "^6.2.8"
   },
   "devDependencies": {
     "@types/compression": "^1.8.1",
     "@types/express": "^5.0.0",
     "@types/node": "^22.0.0",
     "@types/pg": "^8.0.0",
+    "@types/swagger-jsdoc": "^6.0.4",
     "tsx": "^4.0.0",
     "typescript": "^5.6.0"
   }