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/present.go

@@ -9,6 +9,7 @@ import (
 	"jarl/internal/model"
 	"jarl/internal/render"
 	"jarl/internal/rr"
+	"jarl/internal/version"
 )
 
 func (s *Server) presentZone(st *model.State, z *model.Zone, counts map[int64]int) api.Zone {
@@ -132,7 +133,7 @@ func presentToken(t *model.Token) api.Token {
 }
 
 func (s *Server) whoamiOf(p *auth.Principal, se *model.Session) api.Whoami {
-	out := api.Whoami{User: presentUser(p.User), Method: p.Method, Permissions: p.Summary(), Admin: p.IsAdmin(), Version: s.cfg.Version}
+	out := api.Whoami{User: presentUser(p.User), Method: p.Method, Permissions: p.Summary(), Admin: p.IsAdmin(), Version: s.cfg.Version, Build: version.Info()}
 	if p.Token != nil {
 		t := presentToken(p.Token)
 		out.Token = &t