ci: publish separate extension archives

- Rename the keyed extension package to a testing archive to make its purpose explicit.
- Keep the webstore archive as a separate keyless package for Chrome Web Store upload.
- Upload both extension archives to tagged releases instead of only publishing one ambiguous asset.
- Update the package helper's default suffix and documentation to match the release asset names.

scripts/package_extension.py

@@ -1,7 +1,7 @@
 #!/usr/bin/env python3
 """Package the Chrome extension.
 
-Default builds a local/unpacked-style archive that keeps manifest.key so the
+Default builds a testing/unpacked-style archive that keeps manifest.key so the
 extension ID stays stable for native messaging. ``--webstore`` writes the same
 runtime files but strips ``key`` from manifest.json because the Chrome Web Store
 rejects that field.
@@ -40,7 +40,7 @@ def _copy_tree(src: Path, dst: Path) -> None:
 def package_extension(*, webstore: bool = False, out: Path | None = None) -> Path:
   manifest = _read_manifest(webstore)
   version = manifest["version"]
-  suffix = "webstore" if webstore else "local"
+  suffix = "webstore" if webstore else "testing"
   out = out or DIST_DIR / f"browser-cli-extension-{suffix}-v{version}.zip"
   staging = DIST_DIR / f"extension-package-{suffix}"