fix: local timezone for replies + quiet-hours; guard presence "ago" overflow

Timezone: the container ran in UTC, so mavend answered clock/date queries
(voice.go replySystem) and evaluated quiet-hours (gather.go) in UTC. Fixed at
the root — process TZ — rather than per-call: TZ=Europe/Samara in compose +
tzdata in the image (debian-slim strips it, without which Go ignores TZ and
stays UTC). One knob fixes replies and quiet-hours for every daemon; change the
zone in compose.

Overflow: the dash "ago" helper ran time.Since on a zero timestamp (no presence
yet / fresh db), saturating to ~292y and rendering "2562047h47m…". Guard zero →
"never".

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

cmd/mavweb/main.go

@@ -50,7 +50,14 @@ var dashHTML string
 // text in facts/nudges. Read-only: browses the append-only store via CoreAPI,
 // never writes — the store IS the audit trail, this just shows it.
 var dashTmpl = template.Must(template.New("dash").Funcs(template.FuncMap{
-	"ago": func(t time.Time) string { return time.Since(t).Round(time.Second).String() + " ago" },
+	"ago": func(t time.Time) string {
+		// A zero timestamp (no presence signal yet, fresh DB) would make
+		// time.Since saturate to ~292y (MaxInt64) and render as garbage.
+		if t.IsZero() {
+			return "never"
+		}
+		return time.Since(t).Round(time.Second).String() + " ago"
+	},
 }).Parse(dashHTML))
 
 func noCache(h http.Handler) http.Handler {