feat: add template system for role contexts and messages

Implements gt-u1j.20: Prompt templates using go:embed.

- Add internal/templates package with embedded .md.tmpl files
- Role templates: mayor, witness, refinery, polecat, crew
- Message templates: spawn, nudge, escalation, handoff
- Update gt prime to use templates with fallback to hardcoded output
- Add crew role detection for <rig>/crew/<name>/ paths
- Include Gas Town architecture overview in all role contexts

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

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

internal/templates/messages/escalation.md.tmpl

@@ -0,0 +1,29 @@
+# Escalation: {{ .Polecat }} stuck on {{ .Issue }}
+
+## Summary
+
+Polecat **{{ .Polecat }}** appears stuck and has not responded to {{ .NudgeCount }} nudges.
+
+## Details
+
+- **Issue**: {{ .Issue }}
+- **Reason**: {{ .Reason }}
+- **Last known status**: {{ .LastStatus }}
+- **Nudges sent**: {{ .NudgeCount }}
+
+## Possible Actions
+
+{{ range .Suggestions }}
+- {{ . }}
+{{ end }}
+
+## Witness Assessment
+
+The polecat may need:
+- Manual intervention to unblock
+- Session restart to recover from bad state
+- Issue reassignment to a different worker
+
+Please advise on how to proceed.
+
+—Witness

internal/templates/messages/handoff.md.tmpl

@@ -0,0 +1,33 @@
+# 🤝 HANDOFF: {{ .Role }} Session
+
+## Current State
+
+**Role**: {{ .Role }}
+**Working on**: {{ .CurrentWork }}
+**Status**: {{ .Status }}
+
+{{ if .GitBranch }}
+**Git branch**: {{ .GitBranch }}
+{{ if .GitDirty }}⚠️ Working tree has uncommitted changes{{ end }}
+{{ end }}
+
+{{ if .PendingMail }}
+**Pending mail**: {{ .PendingMail }} messages in inbox
+{{ end }}
+
+## Next Steps
+
+{{ range $i, $step := .NextSteps }}
+{{ $i }}. {{ $step }}
+{{ end }}
+
+{{ if .Notes }}
+## Notes
+
+{{ .Notes }}
+{{ end }}
+
+---
+
+This handoff was generated automatically. Read the above carefully and continue
+where the previous session left off.

internal/templates/messages/nudge.md.tmpl

@@ -0,0 +1,33 @@
+# Nudge: Check-in on {{ .Issue }}
+
+Hey {{ .Polecat }},
+
+This is nudge **{{ .NudgeCount }}/{{ .MaxNudges }}** for your current work.
+
+## Reason
+
+{{ .Reason }}
+
+## Current Status
+
+Issue: {{ .Issue }}
+Status: {{ .Status }}
+
+## Action Needed
+
+Please either:
+
+1. **If making progress**: Continue working and signal when done with `gt done`
+2. **If blocked**: File a blocking issue with `bd create --title="Blocked: <reason>" --type=task`
+3. **If done**: Make sure to run:
+   - `bd close {{ .Issue }}`
+   - `bd sync`
+   - `gt done`
+
+## Important
+
+After {{ .MaxNudges }} nudges without progress, this will be escalated to the Mayor.
+
+Please respond or take action.
+
+—Witness

internal/templates/messages/spawn.md.tmpl

@@ -0,0 +1,33 @@
+# Work Assignment
+
+You have been assigned to work on the following issue:
+
+## Issue: {{ .Issue }}
+
+**Title**: {{ .Title }}
+**Priority**: P{{ .Priority }}
+**Branch**: {{ .Branch }}
+
+{{ if .Description }}
+## Description
+
+{{ .Description }}
+{{ end }}
+
+## Your Task
+
+1. Review the issue details with `bd show {{ .Issue }}`
+2. Work in your clone at `{{ .RigName }}/polecats/{{ .Polecat }}/`
+3. Commit changes regularly with clear messages
+4. When complete, run:
+   - `bd close {{ .Issue }}`
+   - `bd sync`
+   - `gt done`
+
+## Need Help?
+
+- File blocking issues: `bd create --title="Blocked: <reason>" --type=task`
+- Ask Witness: `gt mail send {{ .RigName }}/witness -s "Question" -m "..."`
+- Escalate: The Witness will escalate if you're stuck
+
+Good luck!