fix: update flake.nix vendorHash after dependency bumps (bd-gmf)

The Nix flake CI was failing due to stale vendorHash after dependabot
updates to go.mod/go.sum (wazero, anthropic-sdk-go, etc.).

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

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

default.nix

@@ -9,7 +9,7 @@ pkgs.buildGoModule {
   subPackages = [ "cmd/bd" ];
   doCheck = false;
   # Go module dependencies hash (computed via nix build)
-  vendorHash = "sha256-5p4bHTBB6X30FosIn6rkMDJoap8tOvB7bLmVKsy09D8=";
+  vendorHash = "sha256-iTPi8+pbKr2Q352hzvIOGL2EneF9agrDmBwTLMUjDBE=";
 
   # Git is required for tests
   nativeBuildInputs = [ pkgs.git ];