feat(date-time): standardize time context and tool timestamps

docs/concepts/system-prompt.md

@@ -20,7 +20,7 @@ The prompt is intentionally compact and uses fixed sections:
 - **Workspace**: working directory (`agents.defaults.workspace`).
 - **Workspace Files (injected)**: indicates bootstrap files are included below.
 - **Sandbox** (when enabled): indicates sandboxed runtime, sandbox paths, and whether elevated exec is available.
-- **Time**: UTC default + the user’s local time (already converted).
+- **Current Date & Time**: user-local time, timezone, and time format.
 - **Reply Tags**: optional reply tag syntax for supported providers.
 - **Heartbeats**: heartbeat prompt and ack behavior.
 - **Runtime**: host, OS, node, model, thinking level (one line).
@@ -46,12 +46,19 @@ To inspect how much each injected file contributes (raw vs injected, truncation,
 
 ## Time handling
 
-The Time line is compact and explicit:
+The system prompt includes a dedicated **Current Date & Time** section when user
+time or timezone is known. It is explicit about:
 
-- Assume timestamps are **UTC** unless stated.
-- The listed **user time** is already converted to `agents.defaults.userTimezone` (if set).
+- The user’s **local time** (already converted).
+- The **time zone** used for the conversion.
+- The **time format** (12-hour / 24-hour).
 
-Use `agents.defaults.userTimezone` in `~/.clawdbot/clawdbot.json` to change the user time zone.
+Configure with:
+
+- `agents.defaults.userTimezone`
+- `agents.defaults.timeFormat` (`auto` | `12` | `24`)
+
+See [Date & Time](/date-time) for full behavior details.
 
 ## Skills