fix: deduplicate CI watchers and remove task ID from watcher prompts

Prevent duplicate CI completion notifications in paired rooms by checking
for existing active watchers with the same channel+provider+metadata before
creating a new one. Remove Task ID from watcher prompt construction to
avoid router secret redaction (task- IDs contain sk- pattern), passing
EJCLAW_RUNTIME_TASK_ID via env var instead and making cancel_task
auto-resolve when task_id is omitted.

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

src/task-watch-status.ts

@@ -27,7 +27,7 @@ export function isTaskStatusControlMessage(content: string): boolean {
 }
 
 export function extractWatchCiTarget(prompt: string): string | null {
-  const match = prompt.match(/Watch target:\n([\s\S]*?)\n\nTask ID:/);
+  const match = prompt.match(/Watch target:\n([\s\S]*?)\n\nCheck instructions:/);
   return match?.[1]?.trim() || null;
 }