ci: add pull request validation workflow

[xiwangly2]

Summary

This PR adds a separate CI workflow for regular contribution validation, based on upstream/main and independent from the current riscv64 Draft PR.

Changes

• Add .github/workflows/ci.yml for PR, main push, and manual validation.
• Run server npm ci, npm test, and npm run build.
• Run client npm ci, npm test, and npm run build.
• Add a root project-scripts job for package script syntax checks and build version resolution.
• Switch release package workflow dependency installs from npm install to npm ci and cache all lockfiles.
• Update CI/CD docs to match the actual workflow files.
• Fix the existing client chunk-upload test baseline so frontend tests can run reliably in CI.

Validation

• git diff --check
• workflow YAML parse check for .github/workflows/ci.yml and .github/workflows/build.yml
• node --check scripts/package.js
• node --check scripts/resolve-build-version.js
• node scripts/resolve-build-version.js
• cd server && npm test
• cd server && npm run build
• cd client && npm test
• cd client && npm run build

Note: client build still reports the existing Vite chunk/static-dynamic import warnings, but the build exits successfully.