chore: fold --maxWorkers=2 into test:coverage script

Restores parity between `npm test` and `npm run test:coverage` under the
R-v0.7-NEW-8 SIGINT-mid-cadence flake umbrella. The default vitest worker
auto-scaling hit `item-watch.test.ts` SIGINT-test flakes on 2 of 3
consecutive `test:coverage` runs at the v0.10 release-prep close-docs
gate (R-v0.10-NEW-4, filed 2026-05-22). Re-running with the documented
`--maxWorkers=2` workaround stabilised cleanly with 4270 + 4 skipped,
branches 95.89%, functions 98.97% (1354/1368). The underlying timing-race
surface (R-v0.7-NEW-8) is unaddressed by this fold — this only restores
the parity-on-touch property between the two test invocations.

Folded as a work-of-opportunity at v0.11 candidate-selection per the
2026-05-22 user binding; status flip filed in the next docs commit.

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

Author: Nick Webster

package.json

@@ -52,7 +52,7 @@
     "lint:fix": "eslint . --fix",
     "test": "vitest run",
     "test:watch": "vitest watch",
-    "test:coverage": "vitest run --coverage",
+    "test:coverage": "vitest run --coverage --maxWorkers=2",
     "test:unit": "vitest run tests/unit",
     "test:integration": "vitest run tests/integration",
     "test:e2e": "vitest run tests/e2e",