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>

src/metrics/registry.ts

@@ -172,3 +172,66 @@ export const billingLimitRejectionsTotal = new Counter({
   labelNames: ['tenant_id', 'limit_type'] as const,
   registers: [metricsRegistry],
 });
+
+// ────────────────────────────────────────────────────────────────
+// Phase 5 — WS2: A2A Delegation Metrics
+// ────────────────────────────────────────────────────────────────
+
+/**
+ * Total number of A2A delegation chains created.
+ * Labels: tenant_id
+ */
+export const delegationsCreatedTotal = new Counter({
+  name: 'agentidp_delegations_created_total',
+  help: 'Total number of A2A delegation chains created.',
+  labelNames: ['tenant_id'] as const,
+  registers: [metricsRegistry],
+});
+
+/**
+ * Total number of A2A delegation verifications performed.
+ * Labels: tenant_id, result (valid | invalid | expired | revoked)
+ */
+export const delegationsVerifiedTotal = new Counter({
+  name: 'agentidp_delegations_verified_total',
+  help: 'Total number of A2A delegation verifications, labelled by outcome.',
+  labelNames: ['tenant_id', 'result'] as const,
+  registers: [metricsRegistry],
+});
+
+/**
+ * Total number of A2A delegation chains revoked.
+ * Labels: tenant_id
+ */
+export const delegationsRevokedTotal = new Counter({
+  name: 'agentidp_delegations_revoked_total',
+  help: 'Total number of A2A delegation chains revoked.',
+  labelNames: ['tenant_id'] as const,
+  registers: [metricsRegistry],
+});
+
+// ────────────────────────────────────────────────────────────────
+// Phase 5 — WS5: Scaffold Metrics
+// ────────────────────────────────────────────────────────────────
+
+/**
+ * Total number of scaffold ZIPs generated, labelled by language.
+ */
+export const scaffoldGeneratedTotal = new Counter({
+  name: 'agentidp_scaffold_generated_total',
+  help: 'Total number of scaffold ZIPs generated by target language.',
+  labelNames: ['language'] as const,
+  registers: [metricsRegistry],
+});
+
+/**
+ * Duration of scaffold ZIP generation in milliseconds.
+ * Labels: language
+ */
+export const scaffoldGenerationDurationMs = new Histogram({
+  name: 'agentidp_scaffold_generation_duration_ms',
+  help: 'Time taken to generate a scaffold ZIP archive in milliseconds.',
+  labelNames: ['language'] as const,
+  buckets: [10, 50, 100, 250, 500, 1000, 2500],
+  registers: [metricsRegistry],
+});