Merge branch 'feat/footer-share-ci' into dev

CI keeps the 'test once per code state' plan but records commit and
git tree as image labels instead of extra :sha-/:tree- tags, so the
registry only holds dev, latest, vX.Y.Z and stable; the plan test now
asserts the expected decisions.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/api/server.go

@@ -316,6 +316,11 @@ func (s *Server) Router() http.Handler {
 		})
 	})
 
+	// Web Share Target fallback when service worker is not active yet: redirect to /
+	r.Post("/share-target", func(w http.ResponseWriter, r *http.Request) {
+		http.Redirect(w, r, "/", http.StatusSeeOther)
+	})
+
 	// Embedded Frontend SPA Handler
 	if s.staticFS != nil {
 		fileServer := http.FileServer(http.FS(s.staticFS))