Chore: Web client CI pipeline

[FadyGergesRezk]

Enhance the existing web client GitHub Actions pipeline so every pull request runs typecheck, lint, and build with path-aware triggers.

Priority: P1

Tasks

• Update the existing web-client CI job (or extract to web-client-ci.yml) with pull request path filtering for web-client/**
• Job steps:
  • Install dependencies with pnpm install --frozen-lockfile
  • Run pnpm typecheck (tsc --noEmit)
  • Run pnpm lint (ESLint)
  • Run pnpm build (Vite production build)
• Keep pnpm store caching using the existing cache key pattern
• Fail the PR if any step exits non-zero

Acceptance criteria

• A pull request that introduces a TypeScript type error fails CI
• A pull request that introduces an ESLint violation fails CI
• A pull request that breaks the Vite build fails CI
• Passing PRs show a green web-client check
• PRs with no web-client/** changes do not run unnecessary web-client steps