ci: add project regression checks

[JustYannicc]

What changed

Added a lightweight root Project Checks GitHub Actions workflow for pull requests, pushes to main, and manual runs.

The workflow runs on Node 22 with npm caching and covers:

• npm test
• npm run check:i18n
• npm run build:main
• npm run build:renderer

It installs dependencies with native postinstall scripts disabled and skips the live Electron harness on Ubuntu so the job stays focused on fast regression coverage rather than macOS packaging.

Why

The current workflows cover Claude review/assistant flows and the canvas bundle, but do not run the normal root project test/i18n/build checks. That leaves performance cleanup PRs vulnerable to quiet regressions in ranking tests, i18n structure, main-process TypeScript compilation, or renderer bundling.

Compatibility impact

CI-only change. No runtime code, packaged app behavior, or Raycast extension API surface changes.

How tested

• /opt/homebrew/Cellar/node@22/22.22.3/bin/npm ci --ignore-scripts --force
• SUPERCMD_SKIP_ELECTRON_TESTS=1 /opt/homebrew/Cellar/node@22/22.22.3/bin/npm test - 25 tests reported, 24 pass, 1 Electron live test skipped
• /opt/homebrew/Cellar/node@22/22.22.3/bin/npm run check:i18n - exits 0; existing non-strict Italian gaps still warn
• /opt/homebrew/Cellar/node@22/22.22.3/bin/npm run build:main
• /opt/homebrew/Cellar/node@22/22.22.3/bin/npm run build:renderer
• YAML parse smoke test with js-yaml
• Codex LSP: TypeScript diagnostics on vite.config.ts reported no errors; YAML LSP could not run in this local environment because its installed yaml-language-server package is missing vscode-languageserver-protocol

Risks

• npm ci --force is intentional because package.json pins darwin esbuild platform packages for release packaging; without it, npm rejects the lockfile on a single runner platform.
• check:i18n currently treats only configured strict locales as failures, so non-strict locale drift remains a warning unless that script policy changes later.

[JustYannicc]

Superseded by #532 (fix(validation): restore project checks), which consolidates this validation/build change with the related source PRs. Closing this PR in favor of the upstream replacement.