Add pi-coding-agent package, simplify Go builds with unstable.buildGoModule

- Add pi-coding-agent package (v0.55.4) with multi-platform support
- Replace custom Go 1.25.6 override with nixpkgs-unstable buildGoModule
  for beads and perles builds
- Update flake inputs: beads, nixpkgs-unstable, perles
- Update vendor hashes for beads and perles
- Add pi-coding-agent to development role

home/roles/development/default.nix

@@ -8,23 +8,13 @@ let
   # Build beads from flake input
   beadsRev = builtins.substring 0 8 (globalInputs.beads.rev or "unknown");
 
-  # beads' dolt deps require Go >= 1.25.6 (GOTOOLCHAIN=auto can't download in sandbox)
-  go_1_25_6 = pkgs.go_1_25.overrideAttrs (old: rec {
-    version = "1.25.6";
-    src = pkgs.fetchurl {
-      url = "https://go.dev/dl/go${version}.src.tar.gz";
-      hash = "sha256-WMv3ceRNdt5vVtGeM7d9dFoeSJNAkih15GWFuXXCsFk=";
-    };
-  });
-  buildGoModule_1_25_6 = pkgs.buildGoModule.override { go = go_1_25_6; };
-
-  beadsPackage = buildGoModule_1_25_6 {
+  beadsPackage = pkgs.unstable.buildGoModule {
     pname = "beads";
     version = "0.52.0-${beadsRev}";
     src = globalInputs.beads;
     subPackages = [ "cmd/bd" ];
     doCheck = false;
-    vendorHash = "sha256-M+JCxrKgUxCczYzMc2czLZ/JhdVulo7dH2YLTPrJVSc=";
+    vendorHash = "sha256-OL6QGf4xSMpEbmU+41pFdO0Rrs3H162T3pdiW9UfWR0=";
     nativeBuildInputs = [ pkgs.git pkgs.pkg-config ];
     buildInputs = [ pkgs.icu ];
     meta = with lib; {
@@ -79,11 +69,11 @@ let
   # Perles - TUI for beads issue tracking (no upstream flake.nix yet)
   # Source is tracked via flake input for renovate updates
   perlesRev = builtins.substring 0 8 (globalInputs.perles.rev or "unknown");
-  perlesPackage = pkgs.buildGoModule {
+  perlesPackage = pkgs.unstable.buildGoModule {
     pname = "perles";
     version = "unstable-${perlesRev}";
     src = globalInputs.perles;
-    vendorHash = "sha256-JHERJDzbiqgjWXwRhXVjgDEiDQ3AUXRIONotfPF21B0=";
+    vendorHash = "sha256-A5LE9Cor/DRcJtVpiScSoqDYhJIKyaq0cbK+OGmr4XU=";
     doCheck = false;
 
     ldflags = [
@@ -147,6 +137,7 @@ in
 
       # Custom packages
       pkgs.custom.tea-rbw
+      pkgs.custom.pi-coding-agent
     ];
 
     # Install Claude Code humanlayer command and agent plugins