feat: add host-driven GitHub Actions CI watcher (Level 3)

Replace LLM-per-tick polling with direct `gh api` calls for GitHub
Actions watchers. New `ci_provider` discriminator column routes tasks
to either the host-driven path (zero LLM tokens) or the existing
generic LLM path. GitHub watchers poll at 15s intervals (min 10s)
via `checkGitHubActionsRun()` in the scheduler, with completion
messages sent directly to chat on terminal state.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/types.ts

@@ -72,6 +72,8 @@ export interface ScheduledTask {
   group_folder: string;
   chat_jid: string;
   agent_type: AgentType | null;
+  ci_provider?: 'github' | null;
+  ci_metadata?: string | null;
   max_duration_ms?: number | null;
   status_message_id: string | null;
   status_started_at: string | null;