✨ feat(server): /api/info aggregator + frontend version footer

Sprint 2 of autonomous trainer day 2026-05-05. Mistral-implemented
through ICM workspace ship-info-aggregator (bootstrapped backend +
BDD before hitting price limit at stage 02), Claude-completed for
frontend + Playwright + verifier + PR.

Backend:
- GET /api/info aggregator returning version, commit_short, build_date,
  uptime_seconds, cache_enabled, healthz_status (single round trip)
- Optional cache via existing cache service (X-Cache: HIT/MISS)
- BDD scenario @critical covers happy path + version regex; cache
  scenario kept under @skip @bdd-deferred until BDD harness gains a
  cache-enabled mode

Frontend:
- AppFooterView (dumb) + AppFooter (smart wrapper, useFetch) following
  the HealthDashboard / HealthDashboardView pattern
- layouts/default.vue auto-applied via NuxtLayout in app.vue
- humaniseUptime helper in utils/
- Playwright tests use route.fulfill mocking (decoupled from dev-proxy
  infra), assert visible AND content (PR #32 lesson)

Docs:
- documentation/API.md /api/info entry with schema and rationale
- ADR-0026 documents composite endpoint vs separate calls choice

Verifier verdict (skill-driven, audit at stage 04): APPROVE_WITH_NITS.
Nits: handleInfo is 51 lines (could split into builder + emitter);
X-Cache: DISABLED could improve ops clarity.

Out-of-scope follow-up: existing tests/e2e/health.spec.ts happy path
hits the same dev-proxy infra issue as my footer happy path before
mocking. Same fix (server: false + route.fulfill) would apply.

documentation/API.md

@@ -19,6 +19,22 @@ Reference document for all HTTP endpoints exposed by `dance-lessons-coach` serve
 | GET | `/api/healthz` | **Kubernetes-style** rich health: status / version / uptime_seconds / timestamp | PR #20 — handler with swag `@Router /healthz [get]` |
 | GET | `/api/ready` | Readiness check (DB connection + service deps) | `pkg/server/server.go handleReadiness` |
 | GET | `/api/version` | Version info (cached 60s, since PR #29) | `pkg/server/server.go handleVersion` |
+| GET | `/api/info` | **Composite info aggregator**: version / commit_short / build_date / uptime_seconds / cache_enabled / healthz_status. Cached when cache is enabled (X-Cache: HIT/MISS header) | ADR-0026 — `pkg/server/server.go handleInfo` |
+
+`/api/info` body schema (`InfoResponse`):
+
+```json
+{
+  "version": "1.0.0",
+  "commit_short": "abc12345",
+  "build_date": "2026-05-05",
+  "uptime_seconds": 1234,
+  "cache_enabled": true,
+  "healthz_status": "healthy"
+}
+```
+
+Use `/api/info` from a frontend footer or status page when you need version + uptime + cache state in a single round trip. The composite design avoids 3-4 chatty calls (`/version`, `/healthz`, `/ready`) when only a snapshot is needed.
 
 `/api/healthz` body schema (`HealthzResponse`):