Deprecate hook files, use pinned beads for propulsion (gt-rgd9x)

Replace hook file mechanism with discovery-based pinned beads:
- gt hook: now runs bd update <bead> --status=pinned
- gt sling: same, plus nudge to target
- gt handoff: same when bead ID provided
- gt prime: checks pinned beads instead of hook files
- gt mol status: no longer checks hook files

Key changes:
- outputAttachmentStatus: extended to all roles (was Crew/Polecat only)
- checkSlungWork: now queries pinned beads instead of reading hook files
- wisp/io.go functions: marked deprecated with migration notes

This follows Gas Town discovery over explicit state principle.
Hook files are kept for backward compatibility but no longer written.

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

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

internal/wisp/types.go

@@ -1,12 +1,22 @@
 // Package wisp provides hook file support for Gas Town agents.
 //
-// Hooks are used to attach work to an agent for restart-and-resume:
-//   - hook-<agent>.json files track what bead is assigned to an agent
+// DEPRECATED: Hook files are deprecated in favor of pinned beads.
+// Work is now tracked via beads with status=pinned and assignee=agent,
+// which can be discovered via query rather than explicit file management.
+//
+// Commands like `gt hook`, `gt sling`, `gt handoff` now use:
+//
+//	bd update <bead> --status=pinned --assignee=<agent>
+//
+// On session start, agents query for pinned beads rather than reading hook files.
+// This follows Gas Town's "discovery over explicit state" principle.
+//
+// The hook file functions are kept for backward compatibility but are deprecated.
+// Old hook files:
+//   - hook-<agent>.json files tracked what bead was assigned to an agent
 //   - Created by `gt hook`, `gt sling`, `gt handoff`
 //   - Read on session start to restore work context
 //   - Burned after pickup
-//
-// Hook files live in .beads/ alongside other beads data.
 package wisp
 
 import (