fix(quality): register 4 drifted covering tests in stryker tap.testFiles

`check:mutation-test-coverage --strict` has been failing Fast Quality Gates on
every open PR against release/v3.8.51. It grew from 2 missing entries to 5 in
roughly an hour, so it is drifting faster than PRs land.

Four test files cover a mutated module without being listed, so their mutant
kills do not count:

  open-sse/services/accountFallback.ts      <- openai-compatible-per-upstream-402-health
  src/sse/services/auth.ts                  <- openai-compatible-per-upstream-402-health
                                            <- quota-window-label
  src/shared/utils/circuitBreaker.ts        <- combo/execute-target-gates
  open-sse/services/combo/comboStructure.ts <- combo-pin-implicit-allowlist

Registration only — no test or module is touched, and no gate is weakened; the
listing is what makes those kills count in the first place.

Inserted in place, never through a JSON round-trip: re-serializing this file
reorders the ~10 curated entries that are already out of alphabetical order
(learned the hard way in #11438).

check:mutation-test-coverage now reports no drift. check:tracked-artifacts OK,
prettier clean.

Worth noting for whoever adds the next test: this gate fires whenever a NEW test
happens to cover one of the 31 mutated modules, which is easy to do without
realising. Registering it in the same commit is cheaper than a CI round-trip.

stryker.conf.json

@@ -58,6 +58,8 @@
       "tests/unit/account-fallback-retry-after-json.test.ts",
       "tests/unit/account-fallback-route-restriction-403.test.ts",
       "tests/unit/account-fallback-service.test.ts",
+      "tests/unit/combo-pin-implicit-allowlist.test.ts",
+      "tests/unit/combo/execute-target-gates.test.ts",
       "tests/unit/moonshot-quota-writeback.test.ts",
       "tests/unit/accountfallback-ratelimit-400-4976.test.ts",
       "tests/unit/adaptive-admission-route-matrix.test.ts",
@@ -75,6 +77,8 @@
       "tests/unit/api-key-policy-noauth-allowed-connections.test.ts",
       "tests/unit/api-key-rotator-health.test.ts",
       "tests/unit/chat-routing-synced-inventory-11089.test.ts",
+      "tests/unit/openai-compatible-per-upstream-402-health.test.ts",
+      "tests/unit/quota-window-label.test.ts",
       "tests/unit/repro-combo-persisted-cooldown-preskip.test.ts",
       "tests/unit/repro-glm-iso-reset-24h-cap.test.ts",
       "tests/unit/security-route-guard-tiers.test.ts",