docs: update ci parallelization design with implementation status

docs/plans/2026-02-23-ci-parallelization-design.md

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+# CI Parallelization Design
+
+## Overview
+
+Parallelize GitHub Actions workflows to reduce total CI time by running independent tasks concurrently and sharing build artifacts between jobs.
+
+## Scope
+
+- ci.yml
+- release.yml
+- staging.yml
+- nightly.yml
+
+## Approach
+
+Use artifact sharing to avoid redundant builds. Frontend build artifacts are uploaded once and downloaded by dependent jobs.
+
+## Design
+
+### ci.yml
+
+1. **Remove lighthouse dependency** - currently waits for frontend unnecessarily
+2. **Upload frontend artifact** - `frontend` job uploads `dist/`
+3. **Download artifact in test jobs** - `integration`, `e2e`, `regression` download instead of rebuilding
+4. **Split quality job** into 3 parallel jobs:
+   - `coverage` - runs tests with coverage, uploads to Codecov
+   - `bundle-size` - checks bundle size limits
+   - `security` - runs npm audit
+
+Job graph:
+```
+commitlint ──────┐
+frontend ────────┼──► integration
+backend ─────────┤
+                 ├──► e2e
+                 ├──► regression
+                 │
+lighthouse ──────┘ (parallel, no deps)
+
+coverage ──────── (parallel)
+bundle-size ───── (parallel)
+security ──────── (parallel)
+```
+
+### release.yml
+
+Split monolithic job into parallel jobs:
+
+1. **lint** - runs npm run lint
+2. **frontend-test** - runs npm run test:run
+3. **backend-test** - runs backend npm test
+4. **build** - waits for lint + tests, uploads dist artifact
+5. **release** - semantic-release (waits for build)
+6. **docker** - unchanged, waits for release
+
+Job graph:
+```
+lint ──────────┐
+frontend-test ─┼──► build ──► release ──► docker
+backend-test ──┘
+```
+
+### staging.yml
+
+Split into 2 jobs:
+
+1. **test** - lint + frontend tests + backend tests in parallel steps
+2. **deploy** - waits for test, builds and pushes docker
+
+Job graph:
+```
+test ──► deploy
+```
+
+### nightly.yml
+
+Split into 2 jobs:
+
+1. **build** - builds frontend, uploads artifact
+2. **docker** - waits for build, pushes docker image
+
+Job graph:
+```
+build ──► docker
+```
+
+## Implementation Notes
+
+- Use `actions/upload-artifact@v4` and `actions/download-artifact@v4`
+- Artifact retention: 1 day (sufficient for workflow duration)
+- No changes to actual test/build logic, only workflow structure
+
+## Implementation Complete
+
+- [x] Task 1: ci.yml lighthouse parallelization and artifact sharing
+- [x] Task 2: ci.yml quality job split into parallel jobs
+- [x] Task 3: release.yml parallel lint, frontend-test, backend-test, build, release
+- [x] Task 4: staging.yml split into test and deploy jobs
+- [x] Task 5: nightly.yml split into build and docker jobs