fix(deps): update gastown patch and pin beads to Go 1.24 compatible version

- Update gastown-fix-agent-bead-address-title.patch line numbers (326→315)
  for current upstream gastown source
- Remove obsolete gastown patches (rig-prefix, copydir-symlinks) that are
  now handled upstream
- Pin beads to 55e733c (v0.47.2) which uses Go 1.24.0 - newer versions
  require Go 1.25.6 which isn't in nixpkgs-unstable yet
- Remove beads-search-query-optimization.patch as it targets newer code

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

flake.nix

@@ -43,7 +43,9 @@
     };
 
     beads = {
-      url = "github:steveyegge/beads";
+      # Pinned to 55e733c (v0.47.2) - uses Go 1.24.0 which is available in nixpkgs
+      # Later versions require Go 1.25.6 which isn't in nixpkgs-unstable yet
+      url = "github:steveyegge/beads/55e733c";
       inputs.nixpkgs.follows = "nixpkgs-unstable";
     };