feat(phase-5): WS5 — Developer Experience

Implements scaffold ZIP generator, Stoplight Elements API explorer, and CLI scaffold command:

Scaffold API:
- 25 template files for TypeScript/Python/Go/Java/Rust in src/templates/scaffold/
- ScaffoldService: in-memory ZIP via archiver, variable injection (AGENT_ID/NAME/CLIENT_ID/API_URL)
- ScaffoldController: tenant ownership check (403), language validation (400), ZIP stream response
- Route GET /sdk/scaffold/:agentId with rate limiter (10 req/min per tenant)
- Prometheus: scaffold_generated_total + scaffold_generation_duration_ms histogram

Portal:
- Replaced swagger-ui-react with @stoplight/elements API component
- Dynamic import (ssr: false) for browser-only DOM dependency
- Type declarations for @stoplight/elements and CSS module

CLI:
- sentryagent scaffold --agent-id <id> [--language typescript] [--out .]
- Raw fetch for binary ZIP stream → unzipper.Extract() → prints next steps
- Human-readable 400/403/404 error messages

Tests: 19 tests (unit + integration), ScaffoldService 80%+ branch coverage

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

portal/package.json

@@ -9,10 +9,10 @@
     "lint": "next lint"
   },
   "dependencies": {
+    "@stoplight/elements": "^9.0.16",
     "next": "14.2.5",
     "react": "^18.3.1",
-    "react-dom": "^18.3.1",
-    "swagger-ui-react": "^5.17.14"
+    "react-dom": "^18.3.1"
   },
   "devDependencies": {
     "@types/node": "^20.14.0",