✨ 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.

pkg/bdd/steps/common_steps.go

@@ -2,6 +2,7 @@ package steps
 
 import (
 	"fmt"
+	"regexp"
 	"strings"
 
 	"dance-lessons-coach/pkg/bdd/testserver"
@@ -99,3 +100,69 @@ func (s *CommonSteps) theFieldShouldEqual(field, expectedValue string) error {
 	}
 	return nil
 }
+
+// Regex field matching
+func (s *CommonSteps) theFieldShouldMatch(field, pattern string) error {
+	body := string(s.client.GetLastBody())
+	// Extract the value of the field from JSON
+	// Look for "field":"value" and extract value
+	fieldPattern := `"` + field + `":"([^"]*)"`
+	re := regexp.MustCompile(fieldPattern)
+	matches := re.FindStringSubmatch(body)
+	if matches == nil {
+		// Try without quotes (for numbers)
+		fieldPatternNum := `"` + field + `":(\d+\.?\d*)`
+		reNum := regexp.MustCompile(fieldPatternNum)
+		matches = reNum.FindStringSubmatch(body)
+		if matches == nil {
+			return fmt.Errorf("field %q not found in response: %s", field, body)
+		}
+	}
+
+	// matches[1] contains the value
+	value := matches[1]
+
+	// Compile and match the pattern
+	regex, err := regexp.Compile(pattern)
+	if err != nil {
+		return fmt.Errorf("invalid regex pattern %q: %v", pattern, err)
+	}
+
+	if !regex.MatchString(value) {
+		return fmt.Errorf("field %q value %q does not match pattern %q", field, value, pattern)
+	}
+	return nil
+}
+
+// Response is JSON check
+func (s *CommonSteps) theResponseShouldBeJSON() error {
+	body := string(s.client.GetLastBody())
+	// Simple check for JSON structure
+	body = strings.TrimSpace(body)
+	if !strings.HasPrefix(body, "{") && !strings.HasPrefix(body, "[") {
+		return fmt.Errorf("response is not JSON: %s", body)
+	}
+	return nil
+}
+
+// Response contains field (simple string containment in body)
+func (s *CommonSteps) theResponseShouldContain(field string) error {
+	body := string(s.client.GetLastBody())
+	if !strings.Contains(body, `"`+field+`"`) {
+		return fmt.Errorf("response does not contain field %q: %s", field, body)
+	}
+	return nil
+}
+
+// Response header validation
+func (s *CommonSteps) theResponseHeader(header, expectedValue string) error {
+	resp := s.client.GetLastResponse()
+	if resp == nil {
+		return fmt.Errorf("no response captured for header check")
+	}
+	headerValue := resp.Header.Get(header)
+	if headerValue != expectedValue {
+		return fmt.Errorf("header %q expected %q, got %q", header, expectedValue, headerValue)
+	}
+	return nil
+}