docs: refactor README by moving sections to docs/ folder

Move 11 documentation sections to separate markdown files in docs/:
- models.md, load-balancing.md, web-console.md, configuration.md
- menubar-app.md, api-endpoints.md, testing.md, troubleshooting.md
- safety-notices.md, legal.md, development.md

README now contains a Documentation section with links to each doc.
Also moved donation link to above Star History section.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/testing.md

@@ -0,0 +1,24 @@
+# Testing
+
+Run the test suite (requires server running):
+
+```bash
+# Start server in one terminal
+npm start
+
+# Run tests in another terminal
+npm test
+```
+
+Individual tests:
+
+```bash
+npm run test:signatures    # Thinking signatures
+npm run test:multiturn     # Multi-turn with tools
+npm run test:streaming     # Streaming SSE events
+npm run test:interleaved   # Interleaved thinking
+npm run test:images        # Image processing
+npm run test:caching       # Prompt caching
+npm run test:strategies    # Account selection strategies
+npm run test:cache-control # Cache control field stripping
+```