✨ 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.

features/info/info.feature

@@ -0,0 +1,38 @@
+# features/info/info.feature
+@info @critical
+Feature: Info Endpoint
+  The /api/info endpoint should return composite application information
+
+  @basic @critical
+  Scenario: GET /api/info returns all required fields
+    Given the server is running
+    When I request the info endpoint
+    Then the status code should be 200
+    And the response should be JSON
+    And the response should contain "version"
+    And the response should contain "commit_short"
+    And the response should contain "build_date"
+    And the response should contain "uptime_seconds"
+    And the response should contain "cache_enabled"
+    And the response should contain "healthz_status"
+    And the "healthz_status" field should equal "healthy"
+
+  @version @critical
+  Scenario: version field matches semantic version pattern
+    Given the server is running
+    When I request the info endpoint
+    Then the status code should be 200
+    And the "version" field should match /^\d+\.\d+\.\d+$/
+
+  @cache @skip @bdd-deferred
+  Scenario: /api/info is cached when cache is enabled
+    # Deferred: the BDD testsetup currently runs with cache disabled
+    # (see "Cache service disabled" in test logs). Cache HIT/MISS behavior
+    # is covered by unit tests on the cache service. Reopen this scenario
+    # if/when the BDD harness gains a cache-enabled mode (likely after
+    # ADR-0022 Phase 2).
+    Given the server is running with cache enabled
+    When I request the info endpoint
+    Then the response header "X-Cache" should be "MISS"
+    When I request the info endpoint again
+    Then the response header "X-Cache" should be "HIT"

features/info/info_test.go

@@ -0,0 +1,16 @@
+package info
+
+import (
+	"testing"
+
+	"dance-lessons-coach/pkg/bdd/testsetup"
+)
+
+func TestInfoBDD(t *testing.T) {
+	config := testsetup.NewFeatureConfig("info", "progress", false)
+	suite := testsetup.CreateTestSuite(t, config, "dance-lessons-coach BDD Tests - Info Feature")
+
+	if suite.Run() != 0 {
+		t.Fatal("non-zero status returned, failed to run info BDD tests")
+	}
+}