feat: split dirigent_tools into individual tools + human @mention override

Feature 1: Split dirigent_tools
- Replace monolithic dirigent_tools (9 actions) with 9 individual tools
- Discord: dirigent_channel_create, dirigent_channel_update, dirigent_member_list
- Policy: dirigent_policy_get, dirigent_policy_set, dirigent_policy_delete
- Turn: dirigent_turn_status, dirigent_turn_advance, dirigent_turn_reset
- Extract shared executeDiscordAction() helper

Feature 2: Human @mention override
- When humanList user @mentions agents, temporarily override turn order
- Only mentioned agents cycle, ordered by their turn order position
- Original order restores when cycle returns to first agent or all NO_REPLY
- New: setMentionOverride(), hasMentionOverride(), extractMentionedUserIds()
- New: buildUserIdToAccountIdMap() for reverse userId→accountId resolution

Bump version to 0.3.0

plugin/openclaw.plugin.json

@@ -1,7 +1,7 @@
 {
   "id": "dirigent",
   "name": "Dirigent",
-  "version": "0.2.0",
+  "version": "0.3.0",
   "description": "Rule-based no-reply gate with provider/model override and turn management",
   "entry": "./index.ts",
   "configSchema": {