Replace stale bin/install.sh with a wrapper over sync.py restore

bin/install.sh still rsynced --delete from a backup path retired in July, so
the documented Linux install both failed and could erase a working tree. Every
step it claimed to do already lives in bin/sync.py, shared with Windows.

Root ./install.sh is now a thin wrapper over `sync.py restore`, so deployment
stays one bash command. It also registers ncp/promethean in ~/.bashrc, which
was the only thing the old script uniquely did.

Split restore-linux.sh into runtime (Ollama binary, shell aliases) and desktop
(XFCE panel, theme, os-release). Only desktop writes outside the repo, it now
auto-skips off XFCE, and `--no-desktop` skips it explicitly. Two tests keep the
stage names in sync and the $HOME writes confined to the desktop stage.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -72,8 +72,9 @@ does all inference over HTTP).
 ### Linux
 
 ```bash
-# 1. Install deps into the Promethean venv (auto-selects AMD/NVIDIA/CPU)
-./bin/install.sh
+# 1. Build everything: venv (auto-selects AMD/NVIDIA/CPU), web UI, memory DB,
+#    system packages and the Ollama binary.
+./install.sh
 
 # 2. Launch (memory :8001, backend :8000 — backend also serves the built UI)
 ./launch_nexus.sh
@@ -82,7 +83,12 @@ does all inference over HTTP).
 Python deps are layered: `requirements-base.txt` (GPU-agnostic core) plus one
 GPU overlay — `requirements-amd.txt` (ROCm) or `requirements-nvidia.txt` (CUDA).
 `requirements-wsl.txt` is the standalone CPU-only runtime (no base overlay).
-`bin/install.sh` picks the right one for the host.
+`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
+wiring (that stage is auto-skipped off XFCE anyway). It's a thin wrapper over
+`bin/sync.py restore`, the same code the Windows box runs.
 
 ### Individual services