🤖 ci: consolidate workflows into pr.yml with paths-filter

Consolidate ci.yml and build.yml into a single pr.yml workflow with
selective execution based on changed files.

Changes:
- Rename ci.yml → pr.yml, merge in build.yml jobs
- Add dorny/paths-filter to detect docs-only PRs
- Skip all tests/builds for docs-only changes
- Consistent job naming: Test/*, Build/*, Smoke/*
- Single 'required' job for branch protection

Job structure:
- changes: detect docs-only PRs
- static-check: lint, typecheck, fmt
- test-unit, test-integration, test-storybook, test-e2e
- smoke-server, smoke-docker (merge_group only)
- build-linux, build-macos, build-vscode
- codex-comments
- required: aggregates all job results

Configure branch protection to require only 'PR / Required'.

_Generated with `mux`_

Author: ammar-agent