Refinery as worktree: local MR integration (gt-4u5z)

Architecture changes:
- Refinery created as worktree of mayor clone (shares .git)
- Polecat branches stay local (never pushed to origin)
- MRs stored as wisps in .beads-wisp/mq/ (ephemeral)
- Only main gets pushed to origin after merge

New mrqueue package for wisp-based MR storage.
Updated spawn, done, mq_submit, refinery, molecule templates.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/beads/molecules_session.go

@@ -409,9 +409,9 @@ End session with proper handoff.
 1. Sync all state:
 ` + "```" + `bash
 git add -A && git commit -m "WIP: <summary>" || true
-git push origin HEAD
 bd sync
 ` + "```" + `
+Note: Branch stays local (commits saved in shared .git).
 
 2. Write handoff to successor (yourself):
 ` + "```" + `bash
@@ -522,8 +522,8 @@ Finalize session and request termination.
 1. Sync all state:
 ` + "```" + `bash
 bd sync
-git push origin HEAD
 ` + "```" + `
+Note: Branch stays local (commits saved in shared .git).
 
 2. Update work mol based on exit type:
    - COMPLETED: ` + "`bd close <work-mol-root>`" + `