merge: integrate upstream/main (v1.2.15) into feature/webui

- Resolved conflict in src/constants.js: kept config-driven approach

- Adopted upstream 10-second cooldown default

- Added MAX_EMPTY_RESPONSE_RETRIES constant from upstream

- Incorporated new test files and GitHub issue templates

package.json

@@ -27,7 +27,9 @@
     "test:interleaved": "node tests/test-interleaved-thinking.cjs",
     "test:images": "node tests/test-images.cjs",
     "test:caching": "node tests/test-caching-streaming.cjs",
-    "test:crossmodel": "node tests/test-cross-model-thinking.cjs"
+    "test:crossmodel": "node tests/test-cross-model-thinking.cjs",
+    "test:oauth": "node tests/test-oauth-no-browser.cjs",
+    "test:emptyretry": "node tests/test-empty-response-retry.cjs"
   },
   "keywords": [
     "claude",