perf(ci): cache node_modules, skip npm ci on a hit (WP-30 #1)

actions/cache on node_modules keyed by package-lock.json hash, across all 4
npm-based jobs (frontend, storybook-a11y, e2e, api-client-drift). The if:
guard is what makes this a real speedup: npm ci deletes-then-reinstalls
unconditionally, so caching node_modules alone does nothing unless the
install step is skipped outright on a cache hit.

Unverifiable from this environment — CI timing needs a real Gitea run to
confirm; shipped as its own commit so a red run is easy to bisect/revert.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -25,7 +25,15 @@ jobs:
         with:
           node-version: 24
           cache: npm
+      # WP-30: on a hit, npm ci is skipped entirely (not just faster) — caching node_modules
+      # alone doesn't help since npm ci always deletes-then-reinstalls unconditionally.
+      - id: node-modules-cache
+        uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
+        with:
+          path: node_modules
+          key: node-modules-${{ runner.os }}-${{ hashFiles('package-lock.json') }}
       - run: npm ci --prefer-offline --no-audit --no-fund
+        if: steps.node-modules-cache.outputs.cache-hit != 'true'
       - run: npm run lint
       # Bounded-context + atomic-layer boundaries (WP-38, dependency-cruiser).
       - run: npm run dep:check
@@ -67,7 +75,13 @@ jobs:
         with:
           node-version: 24
           cache: npm
+      - id: node-modules-cache
+        uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
+        with:
+          path: node_modules
+          key: node-modules-${{ runner.os }}-${{ hashFiles('package-lock.json') }}
       - run: npm ci --prefer-offline --no-audit --no-fund
+        if: steps.node-modules-cache.outputs.cache-hit != 'true'
       # Cache the chromium download across runs; `install --with-deps` then only
       # runs the (fast, idempotent) apt deps check on a hit.
       - uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
@@ -122,7 +136,13 @@ jobs:
           path: ~/.nuget/packages
           key: nuget-${{ runner.os }}-${{ hashFiles('**/*.csproj') }}
           restore-keys: nuget-${{ runner.os }}-
+      - id: node-modules-cache
+        uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
+        with:
+          path: node_modules
+          key: node-modules-${{ runner.os }}-${{ hashFiles('package-lock.json') }}
       - run: npm ci --prefer-offline --no-audit --no-fund
+        if: steps.node-modules-cache.outputs.cache-hit != 'true'
       - uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
         with:
           path: ~/.cache/ms-playwright
@@ -175,6 +195,12 @@ jobs:
           path: ~/.nuget/packages
           key: nuget-${{ runner.os }}-${{ hashFiles('**/*.csproj') }}
           restore-keys: nuget-${{ runner.os }}-
+      - id: node-modules-cache
+        uses: actions/cache@0057852bfaa89a56745cba8c7296529d2fc39830 # v4.3.0
+        with:
+          path: node_modules
+          key: node-modules-${{ runner.os }}-${{ hashFiles('package-lock.json') }}
       - run: npm ci --prefer-offline --no-audit --no-fund
+        if: steps.node-modules-cache.outputs.cache-hit != 'true'
       - run: npm run gen:api
       - run: git diff --exit-code src/app/shared/infrastructure/api-client.ts backend/swagger.json