v0.4.1: Code-driven OpenAPI docs via swagger-jsdoc

- Add swagger-jsdoc dependency for auto-generating OpenAPI spec from JSDoc
- Add JSDoc @openapi annotations to all route handlers
- Create scripts/generate-openapi.mjs build step
- OpenAPI spec now auto-generated from code — no manual JSON editing
- All 13 endpoints documented with full parameters
- New demo endpoints documented, signup marked as deprecated
- Updated info description: demo-first, no free tier references
- Dockerfile updated to run openapi generation during build
- Build script updated: npm run build generates spec before compile

src/openapi-extra.yaml

@@ -0,0 +1,63 @@
+paths:
+  /v1/signup/free:
+    post:
+      tags:
+        - Account
+      summary: Free signup (discontinued)
+      description: |
+        Free accounts have been discontinued. Use the demo endpoint for testing
+        or subscribe to Pro for production use.
+      deprecated: true
+      requestBody:
+        content:
+          application/json:
+            schema:
+              type: object
+              properties:
+                email:
+                  type: string
+                  format: email
+      responses:
+        '410':
+          description: Free accounts discontinued
+          content:
+            application/json:
+              schema:
+                type: object
+                properties:
+                  error:
+                    type: string
+                    example: 'Free accounts have been discontinued.'
+                  demo_endpoint:
+                    type: string
+                    example: '/v1/demo/html'
+                  pro_url:
+                    type: string
+                    example: 'https://docfast.dev/#pricing'
+  /v1/usage:
+    get:
+      tags:
+        - System
+      summary: Usage statistics (admin only)
+      description: Returns usage statistics for the authenticated user. Requires admin API key.
+      security:
+        - BearerAuth: []
+        - ApiKeyHeader: []
+      responses:
+        '200':
+          description: Usage statistics
+          content:
+            application/json:
+              schema:
+                type: object
+                additionalProperties:
+                  type: object
+                  properties:
+                    count:
+                      type: integer
+                    month:
+                      type: string
+        '403':
+          description: Admin access required
+        '503':
+          description: Admin access not configured