chore(knip): drop dead entry pattern and fail on config hints

examples/acp-agent has no src/ directory — its plugins come from real
packages wired via cordis.yml, and its only local entry (start.ts) is
already auto-discovered. The examples/acp-agent/src/*.ts entry pattern
matched nothing, which knip surfaced as a config hint that exited 0 and
so went unnoticed.

Remove the dead pattern, and pass --treat-config-hints-as-errors so a
future stale entry (a renamed/removed path) fails the hygiene gate
instead of degrading to a silent hint.

package.json

@@ -21,7 +21,7 @@
     "test:e2e": "vitest run --config vitest.e2e.config.ts",
     "test:snapshot": "vitest run --config vitest.snapshot.config.ts",
     "test:snapshot:record": "DSH_SNAPSHOT=record vitest run --config vitest.snapshot.config.ts --update",
-    "knip": "knip",
+    "knip": "knip --treat-config-hints-as-errors",
     "publint": "tsx scripts/publint-all.ts",
     "doc-typecheck": "tsx scripts/doc-typecheck.ts",
     "verify-md-wrap": "tsx scripts/verify-md-wrap.ts",