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

docs/concepts/timezone.md

@@ -19,10 +19,15 @@ Inbound messages are wrapped in an envelope like:
 
 The timestamp in the envelope is **always UTC**, with minutes precision.
 
-## Tool payloads (raw provider data)
+## Tool payloads (raw provider data + normalized fields)
 
 Tool calls (`channels.discord.readMessages`, `channels.slack.readMessages`, etc.) return **raw provider timestamps**.
-These are typically UTC ISO strings (Discord) or UTC epoch strings (Slack). We do not rewrite them.
+We also attach normalized fields for consistency:
+
+- `timestampMs` (UTC epoch milliseconds)
+- `timestampUtc` (ISO 8601 UTC string)
+
+Raw provider fields are preserved.
 
 ## User timezone for the system prompt
 
@@ -31,10 +36,14 @@ unset, Clawdbot resolves the **host timezone at runtime** (no config write).
 
 ```json5
 {
-  agent: { userTimezone: "America/Chicago" }
+  agents: { defaults: { userTimezone: "America/Chicago" } }
 }
 ```
 
 The system prompt includes:
-- `User timezone: America/Chicago`
-- `Current user time: 2026-01-05 15:26`
+- `Current Date & Time` section with local time and timezone
+- `Time format: 12-hour` or `24-hour`
+
+You can control the prompt format with `agents.defaults.timeFormat` (`auto` | `12` | `24`).
+
+See [Date & Time](/date-time) for the full behavior and examples.