Protect release confidence with live agent baselines

The desktop product needs a repeatable local gate that can prove the core Coding Agent loop still works after changes, not only that unit tests pass. This adds a quality-gate runner with PR, baseline, and release modes, structured reports, explicit quarantine metadata, and fixture-based live baseline cases that can run across provider/model targets.

Constraint: Existing check:pr and CI policy behavior must remain usable while the stronger baseline grows around it
Constraint: Default PR gates must not require real model credentials or provider quota
Rejected: Build a standalone QA platform first | too heavy before the baseline task shape is proven
Rejected: Keep unstable server exclusions hardcoded in run-server-tests | hides quarantine policy from reports and future review
Confidence: medium
Scope-risk: moderate
Directive: Expand baseline cases by adding focused fixtures and verifiers; do not make normal PR checks depend on live providers
Tested: bun test scripts/quality-gate/*.test.ts scripts/quality-gate/baseline/*.test.ts
Tested: bun run check:server
Tested: bun run quality:gate --mode baseline --allow-live --provider-model 2944f963-ce75-45b7-bac1-6e4f57df0970:kimi-k2.6:volc-kimi-k2.6 --provider-model 9c78d3df-7fb5-44c7-8436-3a41c3a59231:MiniMax-M2.7-highspeed:minimax-m2.7
Not-tested: desktop UI browser smoke and native release mode in this commit

.gitignore

@@ -22,6 +22,9 @@ extracted-natives/
 # E2E screenshots
 e2e-*.png
 
+# Quality gate reports
+artifacts/quality-runs/
+
 # Desktop build output
 desktop/dist/
 desktop/build-artifacts/