✨ 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.

frontend/components/AppFooterView.vue

@@ -0,0 +1,45 @@
+<script setup lang="ts">
+import { humaniseUptime } from '~/utils/uptime'
+
+export interface AppInfo {
+  version: string
+  commit_short: string
+  build_date: string
+  uptime_seconds: number
+  cache_enabled: boolean
+  healthz_status: string
+}
+
+defineProps<{
+  data: AppInfo | null | undefined
+  pending: boolean
+  error: { message: string } | null | undefined
+}>()
+</script>
+
+<template>
+  <footer data-testid="app-footer">
+    <p v-if="pending" data-testid="app-footer-pending">v?</p>
+    <p v-else-if="error" data-testid="app-footer-error">v? · info unavailable</p>
+    <p v-else-if="data" data-testid="app-footer-info">
+      <span data-testid="app-footer-version">v{{ data.version }}</span>
+      <span> · commit </span>
+      <span data-testid="app-footer-commit">{{ data.commit_short }}</span>
+      <span> · uptime </span>
+      <span data-testid="app-footer-uptime">{{ humaniseUptime(data.uptime_seconds) }}</span>
+    </p>
+  </footer>
+</template>
+
+<style scoped>
+footer {
+  border-top: 1px solid #ccc;
+  padding: 0.5rem 1rem;
+  font-size: 0.85rem;
+  color: #555;
+  text-align: center;
+}
+footer p {
+  margin: 0;
+}
+</style>