pi-coding-agent: switch to npx tsgo to avoid version mismatch

Recent typescript-go updates introduce stricter regex validation
that triggers TS1501 on older ES targets.
This change switches to npx tsgo to maintain compatibility
with the package's existing tsconfig.

Refs:
- https://github.com/badlogic/pi-mono/blob/v0.62.0/package.json#L38
- https://github.com/badlogic/pi-mono/blob/v0.62.0/packages/tui/src/utils.ts#L32-L34
- https://github.com/microsoft/typescript-go/commit/880a9e9cb99d60f689a860af36f4274b78ac535e

pkgs/by-name/pi/pi-coding-agent/package.nix

@@ -2,7 +2,6 @@
   lib,
   buildNpmPackage,
   fetchFromGitHub,
-  typescript-go,
   nix-update-script,
   versionCheckHook,
   writableTmpDirAsHomeHook,
@@ -28,7 +27,6 @@ buildNpmPackage (finalAttrs: {
   npmRebuildFlags = [ "--ignore-scripts" ];
 
   nativeBuildInputs = [
-    typescript-go
     makeBinaryWrapper
   ];
 
@@ -39,9 +37,9 @@ buildNpmPackage (finalAttrs: {
   buildPhase = ''
     runHook preBuild
 
-    tsgo -p packages/ai/tsconfig.build.json
-    tsgo -p packages/tui/tsconfig.build.json
-    tsgo -p packages/agent/tsconfig.build.json
+    npx tsgo -p packages/ai/tsconfig.build.json
+    npx tsgo -p packages/tui/tsconfig.build.json
+    npx tsgo -p packages/agent/tsconfig.build.json
     npm run build --workspace=packages/coding-agent
 
     runHook postBuild