feat: Standardize agent bead naming to prefix-rig-role-name (gt-zvte2)

Implements canonical naming convention for agent bead IDs:
- Town-level: gt-mayor, gt-deacon (unchanged)
- Rig-level: gt-<rig>-witness, gt-<rig>-refinery (was gt-witness-<rig>)
- Named: gt-<rig>-crew-<name>, gt-<rig>-polecat-<name> (was gt-crew-<rig>-<name>)

Changes:
- Added AgentBeadID helper functions to internal/beads/beads.go
- Updated all ID generation call sites to use helpers
- Fixed session parsing in theme.go, statusline.go, agents.go
- Updated doctor check and fix to use canonical format
- Updated tests for new format

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

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

internal/cmd/statusline.go

@@ -60,8 +60,8 @@ func runStatusLine(cmd *cobra.Command, args []string) error {
 		return runDeaconStatusLine(t)
 	}
 
-	// Witness status line (session naming: gt-witness-<rig>)
-	if role == "witness" || strings.HasPrefix(statusLineSession, "gt-witness-") {
+	// Witness status line (session naming: gt-<rig>-witness)
+	if role == "witness" || strings.HasSuffix(statusLineSession, "-witness") {
 		return runWitnessStatusLine(t, rigName)
 	}
 
@@ -221,9 +221,9 @@ func runDeaconStatusLine(t *tmux.Tmux) error {
 // Shows: polecat count, crew count, mail preview
 func runWitnessStatusLine(t *tmux.Tmux, rigName string) error {
 	if rigName == "" {
-		// Try to extract from session name: gt-witness-<rig>
-		if strings.HasPrefix(statusLineSession, "gt-witness-") {
-			rigName = strings.TrimPrefix(statusLineSession, "gt-witness-")
+		// Try to extract from session name: gt-<rig>-witness
+		if strings.HasSuffix(statusLineSession, "-witness") && strings.HasPrefix(statusLineSession, "gt-") {
+			rigName = strings.TrimPrefix(strings.TrimSuffix(statusLineSession, "-witness"), "gt-")
 		}
 	}