ci(check): add svelte-check and workspace lib tests

svelte-check catches type/template errors Vite's build skips; cargo
test --workspace --lib runs our pure-unit suites (prompt contract,
hallucination filter, preset parsing) without GPU or runtime deps.
Test step is Linux-only so the Windows/macOS legs stay focused on
platform compile coverage.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.github/workflows/check.yml

@@ -128,6 +128,12 @@ jobs:
       - name: cargo check (workspace)
         run: cargo check --workspace --all-targets
 
+      # Library tests only — no runtime/GPU deps. Linux-gated to keep
+      # the macOS + Windows legs focused on compile coverage.
+      - name: cargo test (workspace, libs)
+        if: matrix.os == 'ubuntu-22.04'
+        run: cargo test --workspace --lib
+
   frontend:
     name: svelte build + lint
     runs-on: ubuntu-22.04
@@ -149,3 +155,9 @@ jobs:
       # Svelte/Vite frontend compiles cleanly.
       - name: Build frontend (Vite only)
         run: npm run build
+
+      # svelte-check catches type and template errors that Vite's build
+      # step happily lets through (Vite only type-checks .ts; .svelte
+      # type drift slips past until svelte-check runs).
+      - name: svelte-check
+        run: npm run check