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

src/routes/playground.ts

@@ -16,6 +16,73 @@ const playgroundLimiter = rateLimit({
   keyGenerator: (req) => req.ip || req.socket.remoteAddress || "unknown",
 });
 
+/**
+ * @openapi
+ * /v1/playground:
+ *   post:
+ *     tags: [Playground]
+ *     summary: Free demo screenshot (watermarked)
+ *     description: >
+ *       Take a watermarked screenshot without authentication.
+ *       Limited to 5 requests per hour per IP, max 1920×1080 resolution.
+ *       Perfect for evaluating the API before purchasing a plan.
+ *     operationId: playgroundScreenshot
+ *     requestBody:
+ *       required: true
+ *       content:
+ *         application/json:
+ *           schema:
+ *             type: object
+ *             required: [url]
+ *             properties:
+ *               url:
+ *                 type: string
+ *                 format: uri
+ *                 description: URL to capture
+ *                 example: "https://example.com"
+ *               format:
+ *                 type: string
+ *                 enum: [png, jpeg, webp]
+ *                 default: png
+ *                 description: Output image format
+ *               width:
+ *                 type: integer
+ *                 minimum: 320
+ *                 maximum: 1920
+ *                 default: 1280
+ *                 description: Viewport width (clamped to 1920 max)
+ *               height:
+ *                 type: integer
+ *                 minimum: 200
+ *                 maximum: 1080
+ *                 default: 800
+ *                 description: Viewport height (clamped to 1080 max)
+ *     responses:
+ *       200:
+ *         description: Watermarked screenshot image
+ *         content:
+ *           image/png:
+ *             schema: { type: string, format: binary }
+ *           image/jpeg:
+ *             schema: { type: string, format: binary }
+ *           image/webp:
+ *             schema: { type: string, format: binary }
+ *       400:
+ *         description: Invalid request
+ *         content:
+ *           application/json:
+ *             schema: { $ref: "#/components/schemas/Error" }
+ *       429:
+ *         description: Rate limit exceeded (5/hr)
+ *         content:
+ *           application/json:
+ *             schema: { $ref: "#/components/schemas/Error" }
+ *       503:
+ *         description: Service busy
+ *         content:
+ *           application/json:
+ *             schema: { $ref: "#/components/schemas/Error" }
+ */
 playgroundRouter.post("/", playgroundLimiter, async (req, res) => {
   const { url, format, width, height } = req.body;