Show the build in a footer, linked to its release or commit

The version moves from the header to a "Powered by Jarl" footer. A build
of a release tag (HEAD tagged v<VERSION>, no tracked changes; the release
workflow sets RELEASE_TAG) shows and links the release; any other build
shows and links its commit, marked -modified with uncommitted changes.
jarld version, jarl --version, /status and /auth/whoami report the same.

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

internal/server/h_changes.go

@@ -13,6 +13,7 @@ import (
 	"jarl/internal/engine"
 	"jarl/internal/model"
 	"jarl/internal/store"
+	"jarl/internal/version"
 )
 
 func toRequests(in []api.ChangeRequest) []engine.Request {
@@ -273,7 +274,7 @@ func (s *Server) status(w http.ResponseWriter, r *http.Request, p *auth.Principa
 		}
 	}
 	now := time.Now()
-	resp := api.StatusResponse{Version: s.cfg.Version, Engine: raw(st), Time: now, ExpiringTokens: s.expiringTokens(r.Context(), p, now)}
+	resp := api.StatusResponse{Version: s.cfg.Version, Build: version.Info(), Engine: raw(st), Time: now, ExpiringTokens: s.expiringTokens(r.Context(), p, now)}
 	if p.IsAdmin() {
 		resp.Backup = s.backupStatus(r.Context(), now)
 	}