ci: add pull request checks for app, docs, and Rust builds

[ubugeeei]

Finding

The repository only deploys docs on pushes to main. Pull requests can currently land without validating the Electron app build, render bundle, TypeScript project graph, docs build, or Rust backend/render crates.

Evidence

• .github/workflows/deploy-docs.yml only runs docs deployment on main.
• npm run build, npm run build:render, npm run docs:build, cargo check for backend/render all pass locally and should become PR gates.

Acceptance criteria

• Add a pull_request workflow for Node and Rust checks.
• Use npm ci with lockfile cache.
• Run app build, render build, docs build, and cargo check for backend/render.
• Keep deploy-docs unchanged.

[ubugeeei]

対応済みです。修正は PR #1 / commit 9cf4498 に反映済みです。