feat(policy-file): move channel overrides to standalone channelPoliciesFile with hot reload

plugin/README.md

@@ -29,7 +29,7 @@ Optional:
 - `listMode` (`human-list` | `agent-list`, default `human-list`)
 - `humanList` (default [])
 - `agentList` (default [])
-- `channelPolicies` (per-channel overrides by channelId)
+- `channelPoliciesFile` (per-channel overrides in a standalone JSON file)
 - `bypassUserIds` (deprecated alias of `humanList`)
 - `endSymbols` (default ["🔚"])
 - `enableDiscordControlTool` (default true)
@@ -37,6 +37,8 @@ Optional:
 - `discordControlApiToken`
 - `discordControlCallerId`
 
+Per-channel policy file example: `docs/channel-policies.example.json`.
+
 ## Optional tool: `discord_control`
 
 This plugin now registers an optional tool named `discord_control`.