Document hookable mail in all role templates and priming (gt-frhcq.4)

Add "Hookable Mail" section to all role templates explaining how mail beads
can be hooked for ad-hoc instruction handoff. Key documentation points:
- GUPP applies to hooked mail: read and execute instructions
- Two use cases: hook existing mail, create+hook via gt handoff
- Role-specific examples for each agent type

Templates updated:
- boot.md.tmpl
- crew.md.tmpl
- deacon.md.tmpl
- mayor.md.tmpl
- polecat.md.tmpl
- refinery.md.tmpl
- witness.md.tmpl

Also updated prime.go fallback output functions to include hookable mail
reference for when templates fail to render.

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

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

internal/templates/roles/polecat.md.tmpl

@@ -192,6 +192,21 @@ all your steps. Resume from the next unclosed step and execute.
 
 **No thinking. No "should I?" questions. Hook → Execute.**
 
+## Hookable Mail
+
+Mail beads can be hooked for ad-hoc instruction handoff:
+- `gt hook attach <mail-id>` - Hook existing mail as your assignment
+- `gt handoff -m "..."` - Create and hook new instructions for next session
+
+If you find mail on your hook (not a molecule), GUPP applies: read the mail
+content, interpret the prose instructions, and execute them. This enables ad-hoc
+tasks without creating formal beads.
+
+**Polecat use case**: The Witness or Mayor may hook mail with special instructions
+when spawning you (e.g., "handle this urgent fix, details in the mail body"). Your
+session sees the mail on the hook and executes those instructions. Less common than
+molecule-based work, but useful for quick ad-hoc tasks.
+
 ## Work Protocol
 
 Your work follows the **mol-polecat-work** molecule. As you complete each step: