feat: crew attach auto-detection, worktree polecats, beads mail

- gt crew at: auto-detect crew from cwd, run gt prime after launch
- Polecats now use git worktrees from refinery (faster than clones)
- Updated architecture.md for two-tier beads mail model
- Town beads (gm-*) for Mayor mail/coordination
- Rig .beads/ symlinks to refinery/rig/.beads

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

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

internal/config/types.go

@@ -3,7 +3,7 @@ package config
 
 import "time"
 
-// TownConfig represents the main town configuration (config/town.json).
+// TownConfig represents the main town configuration (mayor/town.json).
 type TownConfig struct {
 	Type      string    `json:"type"`       // "town"
 	Version   int       `json:"version"`    // schema version
@@ -11,7 +11,7 @@ type TownConfig struct {
 	CreatedAt time.Time `json:"created_at"`
 }
 
-// RigsConfig represents the rigs registry (config/rigs.json).
+// RigsConfig represents the rigs registry (mayor/rigs.json).
 type RigsConfig struct {
 	Version int                 `json:"version"`
 	Rigs    map[string]RigEntry `json:"rigs"`