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>

README.md

@@ -134,7 +134,8 @@ ncp web
 Python deps are layered: `requirements-base.txt` (GPU-agnostic core) plus one
 GPU overlay — `requirements-amd.txt` (ROCm) or `requirements-nvidia.txt` (CUDA).
 `requirements-windows.txt` is the standalone CPU-only runtime (no base overlay).
-`bin/sync.py` picks the right one for the host.
+macOS uses `requirements-base.txt` directly, no overlay — see the macOS section
+below. `bin/sync.py` picks the right one for the host.
 
 `./install.sh` is also the update path — re-run it any time to pull the latest
 and rebuild. `--check` dry-runs it; `--no-desktop` skips the XFCE panel/theme
@@ -172,10 +173,38 @@ The app opens at `:8000`; click **Start AI** to launch Ollama. The installer
 uses `requirements-windows.txt` (CPU-only, pure-Python — no ML stack, since Ollama
 does all inference over HTTP).
 
+### macOS
+
+Community-supported — no bundled Ollama binary or XFCE desktop branding (that
+stage is Linux/XFCE-only and already skips itself here), but the
+backend/frontend/Ollama stack itself runs natively, no VM or container needed.
+
+```bash
+# 1. Install Homebrew first if you don't have it: https://brew.sh
+
+# 2. Build everything: Homebrew packages (Python, Node, git, Ollama), venv,
+#    web UI, memory DB.
+./install-macos.sh
+
+# 3. Launch (memory :8001, backend :8000 — backend also serves the built UI)
+./launch_nexus.sh
+```
+
+Ollama here is the Homebrew-installed native binary, not the Linux-only bundled
+one — `OllamaManager` already falls back to `ollama` on PATH when
+`ollama/bin/ollama` doesn't exist, so **Start AI** in the sidebar (or `ollama
+serve` in a terminal) uses it with full Metal GPU acceleration automatically,
+no configuration needed.
+
+`./install-macos.sh` is also the update path, same idea as Linux — re-run it
+any time to pull the latest and rebuild; `--check` dry-runs it. It's a thin
+wrapper over `bin/sync.py restore`, the same code Linux and `ncp restore`
+(any platform) run.
+
 ### Individual services
 
 ```bash
-# Linux
+# Linux / macOS
 source Promethean/bin/activate
 
 uvicorn synapse.main:sio_app          --host 0.0.0.0 --port 8000 --reload   # backend (serves the UI too)
@@ -201,7 +230,7 @@ Nexus's dependencies out of the system Python. To add a package, activate it
 and `pip install` as usual:
 
 ```bash
-# Linux
+# Linux / macOS
 source Promethean/bin/activate
 pip install <package>
 ```
@@ -276,7 +305,9 @@ are the exception (YAML files in `data/playbooks/`). All paths are defined in
 - **Filesystem paths** — `synapse/nexus_config.py`
 - **Frontend API base URL** — `interface/web/src/config.js`
 - **Python deps** — `requirements-base.txt` + amd/nvidia GPU overlay;
-  `requirements-windows.txt` = standalone CPU runtime
+  `requirements-windows.txt` = standalone CPU runtime; macOS uses
+  `requirements-base.txt` with no overlay (Ollama, not this venv, does
+  inference — natively, with Metal)
 
 ## Issues and feature requests