feat(install): ensure db fingerprint during gt install/rig init (GH #25)

Add repo fingerprint migration after bd init to ensure daemon can start.
Legacy databases (pre-0.17.5) lack fingerprint, causing slow gt status.

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

internal/rig/manager.go

@@ -435,6 +435,15 @@ func (m *Manager) initBeads(rigPath, prefix string) error {
 			return writeErr
 		}
 	}
+
+	// Ensure database has repository fingerprint (GH #25).
+	// This is idempotent - safe on both new and legacy (pre-0.17.5) databases.
+	// Without fingerprint, the bd daemon fails to start silently.
+	migrateCmd := exec.Command("bd", "migrate", "--update-repo-id")
+	migrateCmd.Dir = rigPath
+	// Ignore errors - fingerprint is optional for functionality
+	_, _ = migrateCmd.CombinedOutput()
+
 	return nil
 }