feat: standardize timestamps to UTC

src/config/types.ts

@@ -445,7 +445,6 @@ export type RoutingConfig = {
 export type MessagesConfig = {
   messagePrefix?: string; // Prefix added to all inbound messages (default: "[clawdbot]" if no allowFrom, else "")
   responsePrefix?: string; // Prefix auto-added to all outbound replies (e.g., "🦞")
-  timestampPrefix?: boolean | string; // true/false or IANA timezone string (default: true with UTC)
 };
 
 export type BridgeBindMode = "auto" | "lan" | "tailnet" | "loopback";
@@ -672,6 +671,8 @@ export type ClawdbotConfig = {
     imageModel?: string;
     /** Agent working directory (preferred). Used as the default cwd for agent runs. */
     workspace?: string;
+    /** Optional IANA timezone for the user (used in system prompt; defaults to host timezone). */
+    userTimezone?: string;
     /** Optional allowlist for /model (provider/model or model-only). */
     allowedModels?: string[];
     /** Optional model aliases for /model (alias -> provider/model). */