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/troubleshooting.md

@@ -0,0 +1,95 @@
+# Troubleshooting
+
+## Windows: OAuth Port Error (EACCES)
+
+On Windows, the default OAuth callback port (51121) may be reserved by Hyper-V, WSL2, or Docker. If you see:
+
+```
+Error: listen EACCES: permission denied 0.0.0.0:51121
+```
+
+The proxy will automatically try fallback ports (51122-51126). If all ports fail, try these solutions:
+
+### Option 1: Use a Custom Port (Recommended)
+
+Set a custom port outside the reserved range:
+
+```bash
+# Windows PowerShell
+$env:OAUTH_CALLBACK_PORT = "3456"
+antigravity-claude-proxy start
+
+# Windows CMD
+set OAUTH_CALLBACK_PORT=3456
+antigravity-claude-proxy start
+
+# Or add to your .env file
+OAUTH_CALLBACK_PORT=3456
+```
+
+### Option 2: Reset Windows NAT
+
+Run as Administrator:
+
+```powershell
+net stop winnat
+net start winnat
+```
+
+### Option 3: Check Reserved Ports
+
+See which ports are reserved:
+
+```powershell
+netsh interface ipv4 show excludedportrange protocol=tcp
+```
+
+If 51121 is in a reserved range, use Option 1 with a port outside those ranges.
+
+### Option 4: Permanently Exclude Port (Admin)
+
+Reserve the port before Hyper-V claims it (run as Administrator):
+
+```powershell
+netsh int ipv4 add excludedportrange protocol=tcp startport=51121 numberofports=1
+```
+
+> **Note:** The server automatically tries fallback ports (51122-51126) if the primary port fails.
+
+---
+
+## "Could not extract token from Antigravity"
+
+If using single-account mode with Antigravity:
+
+1. Make sure Antigravity app is installed and running
+2. Ensure you're logged in to Antigravity
+
+Or add accounts via OAuth instead: `antigravity-claude-proxy accounts add`
+
+## 401 Authentication Errors
+
+The token might have expired. Try:
+
+```bash
+curl -X POST http://localhost:8080/refresh-token
+```
+
+Or re-authenticate the account:
+
+```bash
+antigravity-claude-proxy accounts
+```
+
+## Rate Limiting (429)
+
+With multiple accounts, the proxy automatically switches to the next available account. With a single account, you'll need to wait for the rate limit to reset.
+
+## Account Shows as "Invalid"
+
+Re-authenticate the account:
+
+```bash
+antigravity-claude-proxy accounts
+# Choose "Re-authenticate" for the invalid account
+```