feat(macos): native install path via Homebrew

install-macos.sh mirrors install.sh's split: every portable step - git pull,
venv, pip with the right overlay, npm build - stays in bin/sync.py, shared
with Linux and Windows. The script only does what sync.py cannot do for
itself on a bare Mac, which is install the Homebrew packages needed before a
Python exists to run sync.py with.

Two stages had to learn about darwin. ensure_exec_bits() keyed off
`os.name == "nt"`, which is false on macOS, so it ran the Linux path; and
requirements() had no darwin branch. linux_stage() now no-ops there, which is
what makes skipping the Ollama fetch correct rather than an omission:
bin/fetch-ollama.sh only ships a Linux x86-64 binary, and _ollama_bin() in
synapse/ollama_manager.py already prefers the bundled copy and falls back to
whatever `ollama` is on PATH. On macOS that is the brewed one, with Metal
acceleration and no flags needed.

The XFCE desktop branding is Linux-only and was already gated off macOS the
same way, so there is nothing to install for it here.

install-macos.sh joins the shell-parse list in bin/check.sh.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -25,6 +25,17 @@ ncp web                                                          # memory :8001
 ```
 This activates the `Promethean` venv and starts the memory service on port 8001 and the Synapse backend on port 8000 (which also serves the built UI). It additionally starts a **Vite dev server** for frontend hot-reload — a Linux-dev convenience, unlike the single-process Windows/production path where the backend serves `dist/` alone. It does **not** start Ollama.
 
+**macOS (community-supported):**
+```bash
+./install-macos.sh   # one-time: Homebrew packages + venv + web build, via bin/sync.py
+./launch_nexus.sh     # same script as Linux - it's plain bash, no Linux-only calls
+```
+No bundled Ollama binary (Linux x86-64 only) and no XFCE desktop branding — both
+already no-op on macOS via `bin/sync.py`'s `linux_stage()`. Ollama is instead the
+Homebrew-installed native binary, picked up automatically because
+`OllamaManager` falls back to `ollama` on PATH when the bundled binary is
+absent; that gets full Metal GPU acceleration with no extra config.
+
 **Individual services via CLI:**
 ```bash
 # From nexus-core/ with Promethean venv active:
@@ -83,7 +94,7 @@ cd interface/web && npm run build
 ## Architecture
 
 ### Python venv
-All Python code runs inside `Promethean/` (a local venv). Always activate it before running backend commands: `source Promethean/bin/activate`. Dependencies are layered: `requirements-base.txt` holds the GPU-agnostic core, and a thin overlay pins the right PyTorch build for the target — `requirements-amd.txt` (ROCm), `requirements-nvidia.txt` (CUDA, generated by `bin/gen-nvidia-reqs.py`), or `requirements-windows.txt` (CPU-only). `bin/sync.py` (`requirements()`) selects NVIDIA, AMD, or CPU/Windows requirements from the host.
+All Python code runs inside `Promethean/` (a local venv). Always activate it before running backend commands: `source Promethean/bin/activate`. Dependencies are layered: `requirements-base.txt` holds the GPU-agnostic core, and a thin overlay pins the right PyTorch build for the target — `requirements-amd.txt` (ROCm), `requirements-nvidia.txt` (CUDA, generated by `bin/gen-nvidia-reqs.py`), or `requirements-windows.txt` (CPU-only). `bin/sync.py` (`requirements()`) selects NVIDIA, AMD, CPU/Windows, or — via an explicit `sys.platform == "darwin"` check, since `os.name` alone can't tell macOS apart from Linux — `requirements-base.txt` with no overlay at all for macOS, from the host.
 
 ### Synapse Backend (`synapse/`)
 FastAPI app at `synapse/main.py`. Key responsibilities: