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>

src/config/zod-schema.session.ts

@@ -24,7 +24,6 @@ export const SessionSchema = z
     identityLinks: z.record(z.string(), z.array(z.string())).optional(),
     resetTriggers: z.array(z.string()).optional(),
     idleMinutes: z.number().int().positive().optional(),
-    heartbeatIdleMinutes: z.number().int().positive().optional(),
     reset: SessionResetConfigSchema.optional(),
     resetByType: z
       .object({
@@ -34,6 +33,7 @@ export const SessionSchema = z
       })
       .strict()
       .optional(),
+    resetByChannel: z.record(z.string(), SessionResetConfigSchema).optional(),
     store: z.string().optional(),
     typingIntervalSeconds: z.number().int().positive().optional(),
     typingMode: z