feat(T-6.5): lighthouse perf pass (≥80 on 8 pages)

[GEOFARL]

Summary

• Wire up Lighthouse CI: pnpm --filter @commit-analyzer/web lh:full builds the web app with stub env, boots the e2e mock API + next start, then audits 8 pages with the Supabase auth cookie pre-set (extraHeaders: { Cookie }). Exits non-zero if any page < 0.80 perf.
• New GitHub Actions workflow .github/workflows/lighthouse.yml runs lh:build + lh on every PR touching apps/web/** or packages/** and uploads lighthouse/ (HTML + JSON + summary.md) as an artifact.
• Perf fix: lazy-load the analytics charts (TimelineChart, QualityTrendChart, QualityDistributionChart, ActivityHeatmap) on the repo-detail page via next/dynamic with ssr: false and skeleton placeholders. CodeMirror was already dynamic.

Local results (desktop preset, perf threshold 0.80)

Page	Perf
landing	91
login	92
dashboard	91
repositories	91
repo-detail	91
generate	94
policies	93
settings	94

Reports also uploaded as lighthouse-reports CI artifact (docs/ is gitignored in this repo, so the committed-reports route was not viable).

Test plan

• pnpm -r typecheck green
• pnpm -r lint green (only pre-existing i18next warnings on shadcn dialog/sheet sr-only labels)
• pnpm --filter @commit-analyzer/web test (message catalogs in sync)
• pnpm --filter @commit-analyzer/web lh:full — all 8 pages ≥ 80
• CI Lighthouse workflow runs against PR

Closes #70