feat(sessions): add channelIdleMinutes config for per-channel session idle durations (#1353)

* feat(sessions): add channelIdleMinutes config for per-channel session idle durations

Add new `channelIdleMinutes` config option to allow different session idle
timeouts per channel. For example, Discord sessions can now be configured
to last 7 days (10080 minutes) while other channels use shorter defaults.

Config example:
  sessions:
    channelIdleMinutes:
      discord: 10080  # 7 days

The channel-specific idle is passed as idleMinutesOverride to the existing
resolveSessionResetPolicy, integrating cleanly with the new reset policy
architecture.

* fix

* feat: add per-channel session reset overrides (#1353) (thanks @cash-echo-bot)

---------

Co-authored-by: Cash Williams <cashwilliams@gmail.com>
Co-authored-by: Peter Steinberger <steipete@gmail.com>

docs/gateway/configuration-examples.md

@@ -151,7 +151,9 @@ Save to `~/.clawdbot/clawdbot.json` and you can DM the bot from that number.
       atHour: 4,
       idleMinutes: 60
     },
-    heartbeatIdleMinutes: 120,
+    resetByChannel: {
+      discord: { mode: "idle", idleMinutes: 10080 }
+    },
     resetTriggers: ["/new", "/reset"],
     store: "~/.clawdbot/agents/default/sessions/sessions.json",
     typingIntervalSeconds: 5,