fix(launch): reliable Windows launcher; feat(ui): compact sidebar, Vite toggle, chat Think toggle

Ported from the private repo via bin/publish.sh, plus a manual catch-up
on files that had drifted out of sync before today:

- launch_nexus.ps1: health-check based restart decisions instead of a
  bare port-listen check (a wedged leftover process squatting a port
  used to look "already running" and block the real service from
  starting), a script-path quoting fix for Start-Process, hidden
  console via a wscript.exe wrapper (bin/launch_nexus_hidden.vbs), and
  a taskbar/window icon for the native app window.
- Sidebar: slim icon+text nav rows instead of bulky bordered buttons,
  tighter spacing throughout.
- Settings: full-width layout, a Vite dev-server Start/Stop toggle
  (synapse/frontend_manager.py + /frontend/* endpoints), and the
  Linux-only Icon Branding section now gated on the new /status
  `platform` field instead of always rendering.
- Chatbot: a Think toggle next to the model picker, so extended
  thinking can be flipped without leaving the chat page.
- management/ncp.py: faster start/stop polling (0.25s steps instead of
  1s), Vite no longer blocks `ncp start` on Linux and is skipped
  outright on Windows.

Note: the private repo also has a Mail (IMAP/SMTP) feature; it's
intentionally not included here, so the Mail-only pieces of main.py,
App.jsx, and requirements-windows.txt were left out of this port.

bin/launch_nexus_hidden.vbs

@@ -0,0 +1,15 @@
+' Truly-hidden entry point for the NexusOS desktop shortcut.
+'
+' powershell.exe -WindowStyle Hidden is not enough on Windows 11: when Windows
+' Terminal is the registered default terminal app, it intercepts console-
+' subsystem processes before the hide flag applies, so a "NexusOS" terminal
+' tab shows up anyway. wscript.exe is a GUI-subsystem host (unlike its sibling
+' cscript.exe), so it never allocates a console in the first place and is not
+' a candidate for that hijack - WScript.Shell.Run's own hidden window style
+' (0) is then respected for the powershell.exe it launches.
+Dim fso, scriptDir, psPath, cmd
+Set fso = CreateObject("Scripting.FileSystemObject")
+scriptDir = fso.GetParentFolderName(WScript.ScriptFullName)
+psPath = fso.GetParentFolderName(scriptDir) & "\launch_nexus.ps1"
+cmd = "powershell.exe -NoProfile -ExecutionPolicy Bypass -WindowStyle Hidden -File """ & psPath & """"
+CreateObject("WScript.Shell").Run cmd, 0, False