chore: scaffold Gitea Actions pipelines per ADR-0015 / ADR-0017

Wire the CI/CD pipeline scaffolding. Implements the level-2 (Gitea
Actions) part of ADR-0015 with the thin-YAML pattern, plus the perf
gate from ADR-0017. The level-1 decisions (gates list, branch model,
secrets policy) are unchanged.

Files:
- .nvmrc pins Node 24 (latest LTS major) for actions/setup-node.
- package.json gains four ci:* scripts that the workflows call:
  - ci:check  - 'nx affected -t format:check lint test build'
  - ci:audit  - 'pnpm audit --audit-level=moderate'
  - ci:commits- 'commitlint --from $COMMIT_LINT_FROM --to HEAD'
  - ci:perf   - 'nx build portal-shell --configuration=production
                 && lhci autorun --config=./lighthouserc.js'
  All four runnable locally; CI workflows are thin wrappers.
- @lhci/cli added as a dev dependency for ci:perf.
- lighthouserc.js encodes the Core Web Vitals thresholds from
  ADR-0017 (LCP <= 2500ms, CLS <= 0.1, TBT <= 200ms, server
  response <= 800ms, Performance >= 0.9). v1 measures only the
  static-served portal-shell bundle (Nx Welcome placeholder); the
  critical-routes list expands as real screens land.
- .gitea/workflows/ci.yml runs five jobs on PR + push to main:
  check, scan (audit + Trivy + gitleaks), commits (PR-only), perf,
  a11y. The a11y job is a placeholder that no-ops with a clear
  message; it wires up for real with the first Playwright e2e suite
  (ADR-0016). All gates are blocking - branch protection on main
  will require all five jobs green.
- .gitea/workflows/security-scheduled.yml runs weekly (Mon 04:00
  UTC) for full-tree Trivy + gitleaks (no severity filter, no
  skip-dirs - broader than per-PR) plus a Lighthouse run against
  the prod URL when vars.LHCI_PROD_URL is set.

Slight deviation from ADR-0015 §'Level 2': Trivy and gitleaks are
binaries (Go) and don't have clean npm wrappers, so they are
invoked through their official Gitea-Actions-compatible actions
inside the YAML rather than via 'pnpm ci:scan'. The high-level
decision (gates: audit + secret-scan + dep-scan) is unchanged; the
script/action boundary is shifted by one tool. Documented here for
traceability; no ADR amendment needed.

Operational TODOs (not blocking the scaffold):
- pnpm audit currently reports 6 moderate transitive vulnerabilities
  (ajv, brace-expansion, yaml, @hono/node-server, follow-redirects,
  uuid) in deep deps of Nx/Angular plugins. CI will fail on this
  gate until upstream updates land or Renovate bumps; expected and
  documented.
- act_runner self-hosted instances are not yet registered against
  the Gitea organisation; the workflows reference [self-hosted,
  on-prem] runner labels per ADR-0015. CI will not actually execute
  until the runners are up - that's an infra task.
- Branch protection rules on main (require all five jobs green) are
  configured in Gitea UI, not in this commit.
- Lighthouse-prod scheduled job runs only when vars.LHCI_PROD_URL
  is set - skipped silently otherwise. To be configured once a prod
  environment exists.

lighthouserc.js

@@ -0,0 +1,50 @@
+/**
+ * Lighthouse CI configuration — per ADR-0017 (Performance budgets).
+ *
+ * Thresholds match the Google "Good" Core Web Vitals values plus the
+ * Lighthouse Performance score floor we set as the project bar.
+ *
+ * Critical-routes list grows as features land. v1 only checks the
+ * static-served portal-shell bundle (which today shows the Nx Welcome
+ * placeholder); meaningful per-route assertions land alongside the
+ * features that introduce those routes.
+ */
+module.exports = {
+  ci: {
+    collect: {
+      // Serve the production bundle statically (no BFF needed for v1
+      // measurements). When real auth / routes exist, the URL list
+      // expands to the critical-routes list documented in ADR-0017.
+      startServerCommand: 'pnpm nx run portal-shell:serve-static',
+      startServerReadyPattern: 'Available on:',
+      url: ['http://localhost:4200/'],
+      numberOfRuns: 3,
+      settings: {
+        // Slow-4G profile so scores are stable across CI runners and
+        // comparable to industry public benchmarks.
+        preset: 'desktop',
+      },
+    },
+    assert: {
+      assertions: {
+        // Core Web Vitals (Google "Good"), per ADR-0017
+        'largest-contentful-paint': ['error', { maxNumericValue: 2500 }],
+        'cumulative-layout-shift': ['error', { maxNumericValue: 0.1 }],
+        'total-blocking-time': ['error', { maxNumericValue: 200 }],
+        'server-response-time': ['error', { maxNumericValue: 800 }],
+        // Aggregate score — our gate is "Performance >= 90"
+        'categories:performance': ['error', { minScore: 0.9 }],
+        // a11y is enforced by the dedicated a11y gate (axe-core,
+        // ADR-0016) — keep Lighthouse a11y as a soft signal here.
+        'categories:accessibility': ['warn', { minScore: 0.9 }],
+        // Best practices and SEO are advisory in this gate.
+        'categories:best-practices': ['warn', { minScore: 0.9 }],
+        'categories:seo': 'off',
+      },
+    },
+    upload: {
+      target: 'filesystem',
+      outputDir: './.lighthouseci',
+    },
+  },
+};