Simplify timestampPrefix: bool or timezone string, default true

- timestampPrefix: true (UTC), false (off), or 'America/New_York'
- Removed separate timestampTimezone option
- Default is now enabled (true/UTC) unless explicitly false

README.md

@@ -169,8 +169,7 @@ warelay supports running on the same phone number you message from—you chat wi
 | `inbound.allowFrom` | `string[]` (default: empty) | E.164 numbers allowed to trigger auto-reply (no `whatsapp:`); `"*"` allows any sender. |
 | `inbound.messagePrefix` | `string` (default: `"[warelay]"` if no allowFrom, else `""`) | Prefix added to all inbound messages before passing to command. |
 | `inbound.responsePrefix` | `string` (default: —) | Prefix auto-added to all outbound replies (e.g., `"🦞"`). |
-| `inbound.timestampPrefix` | `boolean` (default: `false`) | Prepend compact timestamp `[Nov 29 06:30]` to messages. |
-| `inbound.timestampTimezone` | `string` (default: `"UTC"`) | IANA timezone for timestamp (e.g., `"Europe/Vienna"`). |
+| `inbound.timestampPrefix` | `boolean \| string` (default: `true`) | Timestamp prefix: `true` (UTC), `false` (disabled), or IANA timezone like `"Europe/Vienna"`. |
 | `inbound.reply.mode` | `"text"` \| `"command"` (default: —) | Reply style. |
 | `inbound.reply.text` | `string` (default: —) | Used when `mode=text`; templating supported. |
 | `inbound.reply.command` | `string[]` (default: —) | Argv for `mode=command`; each element templated. Stdout (trimmed) is sent. |