feat: rebrand to ZeroGravity, replace proxyctl with zg Rust binary

Phase 1 - Rename:
- Crate: antigravity-proxy -> zerogravity
- Env: ANTIGRAVITY_OAUTH_TOKEN -> ZEROGRAVITY_TOKEN
- Paths: ~/.config/antigravity-proxy -> ~/.config/zerogravity
- Paths: /tmp/antigravity-* -> /tmp/zerogravity-*
- User: antigravity-ls -> zerogravity-ls
- Service: antigravity-proxy -> zerogravity

Phase 2 - zg daemon manager:
- New Rust binary src/bin/zg.rs replaces scripts/proxyctl bash
- Commands: start, stop, restart, rebuild, status, logs, test, health
- Auto-resolves project dir from binary location
- All commands exit immediately (safe for agent fast-bash)

GEMINI.md

@@ -27,41 +27,41 @@ This "LS as dumb relay" pattern keeps the LS interactions minimal and predictabl
 
 ## Agent Quick Reference
 
-### `proxyctl` — Daemon Manager
+### `zg` — Daemon Manager
 
-`proxyctl` commands exit immediately (not foreground) — safe for agent use via fast-bash MCP.
+`zg` commands exit immediately (not foreground) — safe for agent use via fast-bash MCP.
 
 ```bash
 # Rebuild and restart after code changes
-proxyctl restart
+zg restart
 
 # Quick test
-proxyctl test "say hi in 3 words"
+zg test "say hi in 3 words"
 
 # Check status
-proxyctl status
+zg status
 
 # Check health
-proxyctl health
+zg health
 ```
 
 | Command               | Description                         |
 | --------------------- | ----------------------------------- |
-| `proxyctl start`      | Start the proxy daemon              |
-| `proxyctl stop`       | Stop the proxy daemon               |
-| `proxyctl restart`    | Rebuild + restart                   |
-| `proxyctl rebuild`    | Build release binary only           |
-| `proxyctl status`     | Service status + quota + usage      |
-| `proxyctl logs [N]`   | Tail last N lines + follow          |
-| `proxyctl logs-all`   | Full log dump (no follow)           |
-| `proxyctl test [msg]` | Quick test request (gemini-3-flash) |
-| `proxyctl health`     | Health check                        |
+| `zg start`      | Start the proxy daemon              |
+| `zg stop`       | Stop the proxy daemon               |
+| `zg restart`    | Rebuild + restart                   |
+| `zg rebuild`    | Build release binary only           |
+| `zg status`     | Service status + quota + usage      |
+| `zg logs [N]`   | Tail last N lines + follow          |
+| `zg logs-all`   | Full log dump (no follow)           |
+| `zg test [msg]` | Quick test request (gemini-3-flash) |
+| `zg health`     | Health check                        |
 
 ### Testing After Changes
 
 ```bash
 # 1. Rebuild + restart
-proxyctl restart
+zg restart
 
 # 2. Test an endpoint
 curl -s http://localhost:8741/v1/chat/completions \
@@ -69,7 +69,7 @@ curl -s http://localhost:8741/v1/chat/completions \
   -d '{"model": "gemini-3-flash", "messages": [{"role": "user", "content": "Say hi"}]}' | jq .
 
 # 3. Inspect latest trace
-TRACE_DIR=~/.config/antigravity-proxy/traces/$(date +%Y-%m-%d)
+TRACE_DIR=~/.config/zerogravity/traces/$(date +%Y-%m-%d)
 cat "$TRACE_DIR/$(ls -t "$TRACE_DIR" | head -1)/summary.md"
 ```
 
@@ -99,8 +99,8 @@ cat "$TRACE_DIR/$(ls -t "$TRACE_DIR" | head -1)/summary.md"
 
 The proxy needs an OAuth token:
 
-1. **Env var**: `ANTIGRAVITY_OAUTH_TOKEN=ya29.xxx`
-2. **Token file**: `~/.config/antigravity-proxy-token`
+1. **Env var**: `ZEROGRAVITY_TOKEN=ya29.xxx`
+2. **Token file**: `~/.config/zerogravity-token`
 3. **Runtime**: `curl -X POST http://localhost:8741/v1/token -d '{"token":"ya29.xxx"}'`
 
 ## CLI Flags