feat(crew): add crew configuration to rigs.json for cross-machine sync

Add CrewRegistryConfig to RigEntry allowing crew members to be defined
in rigs.json and synced across machines. The new `gt crew sync` command
creates missing crew members from the configuration.

Configuration example:
  "rigs": {
    "gastown": {
      "crew": {
        "theme": "mad-max",
        "members": ["diesel", "chrome", "nitro"]
      }
    }
  }

Closes: gt-tu4

internal/config/types.go

@@ -157,10 +157,11 @@ type RigsConfig struct {
 
 // RigEntry represents a single rig in the registry.
 type RigEntry struct {
-	GitURL      string       `json:"git_url"`
-	LocalRepo   string       `json:"local_repo,omitempty"`
-	AddedAt     time.Time    `json:"added_at"`
-	BeadsConfig *BeadsConfig `json:"beads,omitempty"`
+	GitURL      string              `json:"git_url"`
+	LocalRepo   string              `json:"local_repo,omitempty"`
+	AddedAt     time.Time           `json:"added_at"`
+	BeadsConfig *BeadsConfig        `json:"beads,omitempty"`
+	Crew        *CrewRegistryConfig `json:"crew,omitempty"`
 }
 
 // BeadsConfig represents beads configuration for a rig.
@@ -169,6 +170,18 @@ type BeadsConfig struct {
 	Prefix string `json:"prefix"` // issue prefix
 }
 
+// CrewRegistryConfig represents crew configuration for a rig in rigs.json.
+// This enables cross-machine sync of crew member definitions.
+type CrewRegistryConfig struct {
+	// Theme selects the naming theme for crew members (e.g., "mad-max", "minerals").
+	// Used when displaying crew member names and for consistency across machines.
+	Theme string `json:"theme,omitempty"`
+
+	// Members lists the crew member names to create on this rig.
+	// Use `gt crew sync` to create missing members from this list.
+	Members []string `json:"members,omitempty"`
+}
+
 // CurrentTownVersion is the current schema version for TownConfig.
 // Version 2: Added Owner and PublicName fields for federation identity.
 const CurrentTownVersion = 2