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/load-balancing.md

@@ -0,0 +1,59 @@
+# Multi-Account Load Balancing
+
+When you add multiple accounts, the proxy intelligently distributes requests across them using configurable selection strategies.
+
+## Account Selection Strategies
+
+Choose a strategy based on your needs:
+
+| Strategy | Best For | Description |
+| --- | --- | --- |
+| **Hybrid** (Default) | Most users | Smart selection combining health score, token bucket rate limiting, quota awareness, and LRU freshness |
+| **Sticky** | Prompt caching | Stays on the same account to maximize cache hits, switches only when rate-limited |
+| **Round-Robin** | Even distribution | Cycles through accounts sequentially for balanced load |
+
+**Configure via CLI:**
+
+```bash
+antigravity-claude-proxy start --strategy=hybrid    # Default: smart distribution
+antigravity-claude-proxy start --strategy=sticky    # Cache-optimized
+antigravity-claude-proxy start --strategy=round-robin  # Load-balanced
+```
+
+**Or via WebUI:** Settings → Server → Account Selection Strategy
+
+## How It Works
+
+- **Health Score Tracking**: Accounts earn points for successful requests and lose points for failures/rate-limits
+- **Token Bucket Rate Limiting**: Client-side throttling with regenerating tokens (50 max, 6/minute)
+- **Quota Awareness**: Accounts below configurable quota thresholds are deprioritized; exhausted accounts trigger emergency fallback
+- **Quota Protection**: Set minimum quota levels globally, per-account, or per-model to switch accounts before quota runs out
+- **Emergency Fallback**: When all accounts appear exhausted, bypasses checks with throttle delays (250-500ms)
+- **Automatic Cooldown**: Rate-limited accounts recover automatically after reset time expires
+- **Invalid Account Detection**: Accounts needing re-authentication are marked and skipped
+- **Prompt Caching Support**: Session IDs derived from conversation enable cache hits across turns
+
+## Monitoring
+
+Check account status, subscription tiers, and quota anytime:
+
+```bash
+# Web UI: http://localhost:8080/ (Accounts tab - shows tier badges and quota progress)
+# CLI Table:
+curl "http://localhost:8080/account-limits?format=table"
+```
+
+### CLI Management Reference
+
+If you prefer using the terminal for management:
+
+```bash
+# List all accounts
+antigravity-claude-proxy accounts list
+
+# Verify account health
+antigravity-claude-proxy accounts verify
+
+# Interactive CLI menu
+antigravity-claude-proxy accounts
+```