fix(skills): discover worktree branches dynamically in worktree-update

The skill previously relied on the agent hardcoding branch names,
which missed non-standard branches like planning. Now explicitly
instructs the agent to use git worktree list for discovery.

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

.claude/skills/worktree-update/SKILL.md

@@ -44,10 +44,16 @@ Branch determines the mode: `main` → outbound sync, anything else → inbound
 git fetch --all
 ```
 
+Discover all worktree branches (excluding `main` itself):
+
+```bash
+git worktree list | grep -v '\[main\]' | sed 's/.*\[//;s/\]//'
+```
+
 For each worktree branch, check if it has commits ahead of main:
 
 ```bash
-git rev-list --count main..<branch>
+git rev-list --count main..origin/<branch>
 ```
 
 Skip branches with 0 commits ahead. For branches that ARE ahead, collect: