feat(namepool): Add themed name pools for polecats

Polecats now get themed names from the Mad Max universe by default
(furiosa, nux, slit, etc.) instead of generic polecat-01, polecat-02.

Changes:
- Add NamepoolConfig to config/types.go for per-rig theme configuration
- Update namepool.go with three built-in themes:
  - mad-max (default): furiosa, nux, imperator, etc.
  - minerals: obsidian, quartz, ruby, etc.
  - wasteland: rust, chrome, fury, etc.
- Add gt namepool commands: themes, set, add, reset
- Update manager.go to load namepool config from rig settings

Configuration in .gastown/config.json:
```json
{
  "namepool": {
    "style": "minerals",
    "max_before_numbering": 50
  }
}
```

Issue: beads-rs0

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

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

internal/config/types.go

@@ -53,6 +53,7 @@ type RigConfig struct {
 	Version    int               `json:"version"`               // schema version
 	MergeQueue *MergeQueueConfig `json:"merge_queue,omitempty"` // merge queue settings
 	Theme      *ThemeConfig      `json:"theme,omitempty"`       // tmux theme settings
+	Namepool   *NamepoolConfig   `json:"namepool,omitempty"`    // polecat name pool settings
 }
 
 // ThemeConfig represents tmux theme settings for a rig.
@@ -125,3 +126,26 @@ func DefaultMergeQueueConfig() *MergeQueueConfig {
 		MaxConcurrent:        1,
 	}
 }
+
+// NamepoolConfig represents namepool settings for themed polecat names.
+type NamepoolConfig struct {
+	// Style picks from a built-in theme (e.g., "mad-max", "minerals", "wasteland").
+	// If empty, defaults to "mad-max".
+	Style string `json:"style,omitempty"`
+
+	// Names is a custom list of names to use instead of a built-in theme.
+	// If provided, overrides the Style setting.
+	Names []string `json:"names,omitempty"`
+
+	// MaxBeforeNumbering is when to start appending numbers.
+	// Default is 50. After this many polecats, names become name-01, name-02, etc.
+	MaxBeforeNumbering int `json:"max_before_numbering,omitempty"`
+}
+
+// DefaultNamepoolConfig returns a NamepoolConfig with sensible defaults.
+func DefaultNamepoolConfig() *NamepoolConfig {
+	return &NamepoolConfig{
+		Style:              "mad-max",
+		MaxBeforeNumbering: 50,
+	}
+}