fix(build): exclude *.test.ts from emit so test files aren't shipped

Paperclip's plugin loader links the package as ESM, and dist/ui-parser.test.js
contained `import { parseStdoutLine } from "./ui-parser.js"` — but ui-parser.js
is bundled as CJS (see 480f7cf) so Node's ESM linker can't resolve the named
export. Result: adapter install fails with

    SyntaxError: The requested module './ui-parser.js' does not provide an
    export named 'parseStdoutLine'

Same root cause as c79eea7, just on the test file instead of src/index.ts.

Fix: introduce tsconfig.build.json that extends the base tsconfig and adds
"exclude": ["**/*.test.ts"]. The build script now runs tsc against that
config, so test files don't end up in dist/. tsconfig.json (used by --noEmit
typecheck and vitest) still includes them, so test type-safety is preserved.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -17,7 +17,7 @@
     "dist"
   ],
   "scripts": {
-    "build": "tsc && npm run build:ui-parser",
+    "build": "tsc -p tsconfig.build.json && npm run build:ui-parser",
     "build:ui-parser": "esbuild src/ui-parser.ts --bundle --format=cjs --target=es2020 --outfile=dist/ui-parser.js --log-level=warning",
     "clean": "rm -rf dist",
     "typecheck": "tsc --noEmit",

tsconfig.build.json

@@ -0,0 +1,4 @@
+{
+  "extends": "./tsconfig.json",
+  "exclude": ["**/*.test.ts"]
+}