Fix native macOS tailnet launch and Metal GPU probe (#756)

* macOS/Apple Silicon: detect Metal backend, surface MLX models, brew tmux hint

- hardware.py: add _detect_macos() via sysctl/system_profiler; report
  backend=metal + unified_memory on Apple Silicon instead of cpu_arm
- fit.py: add Apple Silicon (M1-M5) unified-memory bandwidths + metal
  FALLBACK_K so throughput estimates use the real bandwidth formula
- setup.py: Mac-specific 'brew install tmux' hint

Verified on M5 Pro 48GB: backend=metal, 273GB/s matched, 6 MLX models now
visible (were hidden), cuda still hides MLX, no new test failures.

* Fix native macOS tailnet launch and Metal GPU probe

---------

Co-authored-by: Elijah (Hermes) <hermes@local>

README.md

@@ -90,7 +90,14 @@ cd odysseus
 ./start-macos.sh
 ```
 
-It launches at `http://127.0.0.1:7860`. To build a clickable app wrapper:
+It launches at `http://127.0.0.1:7860`. To expose it to your phone over a trusted LAN/VPN such as Tailscale, bind all interfaces:
+
+```bash
+ODYSSEUS_HOST=0.0.0.0 ./start-macos.sh
+# then open http://<tailscale-ip>:7860
+```
+
+Keep auth enabled when binding outside loopback, and do not expose this port directly to the public internet. To build a clickable app wrapper:
 
 ```bash
 ./build-macos-app.sh