test(spice): exclude custom-chip from the static-fixture catalog check

The `custom-chip` SPICE mapper emits its sources from getChipDrivenPins()
(the chip's live driven output pins), so a static pin/property fixture can
never exercise it -- it always returns null. The "every mapped metadataId
has a test fixture" check flagged it as missing a fixture, failing the
suite. Exclude it via a RUNTIME_STATE_MAPPERS set; custom-chip SPICE
behaviour is covered by the chip-bus integration tests.

Pre-existing since 4cb5748 (custom-chip first-class circuit nodes).

frontend/src/__tests__/component-to-spice.test.ts

@@ -222,9 +222,18 @@ describe('PASSIVE_PRESETS — preset variants share their base mapper', () => {
   });
 });
 
+// Mappers whose output depends on live runtime state rather than the static
+// component (pins + properties) a fixture can describe. `custom-chip` emits its
+// SPICE sources from getChipDrivenPins(comp.id) — the chip's currently-driven
+// output pins — so a static fixture always yields null. It is exercised by the
+// chip-bus integration tests instead, not this catalog harness.
+const RUNTIME_STATE_MAPPERS = new Set(['custom-chip']);
+
 describe('componentToSpice — catalog completeness', () => {
   it('every mapped metadataId has a test fixture', () => {
-    const missing = mappedMetadataIds().filter((id) => !MINIMAL_FIXTURES[id]);
+    const missing = mappedMetadataIds().filter(
+      (id) => !MINIMAL_FIXTURES[id] && !RUNTIME_STATE_MAPPERS.has(id),
+    );
     expect(missing, `Missing fixtures for: ${missing.join(', ')}`).toEqual([]);
   });