chore(pack): exclude test files and fixtures from npm package (#2410)

The published tarball ships 601 compiled *.test.js files, ~100 *.test.d.ts,
stray *.test.ts sources, and clis/**/__fixtures__/ HTML snapshots — none of
which are used at runtime. Excluding them shrinks the package from 2340 to
1638 files and from 14.0 MB to 9.2 MB unpacked (tarball 3.1 MB -> 2.2 MB),
which noticeably speeds up npm install.

Verified with npm pack --dry-run against the extracted 1.8.7 tarball
contents: no .test.* or __fixtures__ entries remain.

Co-authored-by: exe.dev user <exedev@koala-fife.exe.xyz>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

package.json

@@ -37,7 +37,9 @@
     "cli-manifest.json",
     "scripts/",
     "README.md",
-    "LICENSE"
+    "LICENSE",
+    "!**/*.test.*",
+    "!**/__fixtures__/"
   ],
   "scripts": {
     "dev": "tsx src/main.ts",