fix: move lock files to test-fixtures, pnpm global-bin-dir, node-based version detection

[mayurrawte]

Fixes all remaining test failures. Three root causes:

1. pnpm-lock.yaml in repo root broke npm/yarn/node-matrix jobs
Angular CLI 19 auto-detects lock files to choose the package manager. Having pnpm-lock.yaml in root caused every npm/yarn test job to fail with: The project is configured to use 'pnpm', but it is not installed or cannot be found.

Fix: moved pnpm-lock.yaml and yarn.lock to .github/test-fixtures/ (Angular CLI only detects root-level lock files). Test workflow now passes cache-dependency-path: .github/test-fixtures/pnpm-lock.yaml for pnpm jobs.

2. pnpm global bin not on PATH
pnpm v9+ puts global bins in {PNPM_HOME}/bin/, but pnpm/action-setup only adds PNPM_HOME itself to PATH. Error: The configured global bin directory is not in PATH.

Fix: pnpm config set global-bin-dir "$PNPM_HOME" before the global install — bins go directly into PNPM_HOME which is already on PATH.

3. Version detection via ng version was unreliable
ng version inside the composite action had PATH timing issues (GITHUB_PATH updates don't take effect within the same composite action) and pipefail edge cases.

Fix: replaced with node -e "require(...package.json).version" — reads the installed @angular/cli/package.json directly via npm root -g / pnpm root -g / yarn global dir. No PATH dependency, works cross-platform.