feat(gui): make desktop setup flow real and testable

Add a GUI-first setup gate and runtime state API so desktop onboarding is safe, iterative, and works with isolated fresh-mode installs. Scaffold and wire the desktop shell/runtime pieces so this branch runs end-to-end without disturbing existing user installs.

apps/gui/dev-tauri.ps1

@@ -0,0 +1,57 @@
+param(
+  [string]$Command = "dev",
+  [switch]$Fresh,
+  [switch]$ResetFresh
+)
+
+$ErrorActionPreference = "Stop"
+Set-ExecutionPolicy -Scope Process -ExecutionPolicy Bypass -Force
+
+$AppRoot = Split-Path -Parent $MyInvocation.MyCommand.Path
+$Script = Join-Path $AppRoot "scripts\tauri.mjs"
+
+if (-not (Get-Command node -ErrorAction SilentlyContinue)) {
+  throw "Windows Node.js was not found. Install it with: winget install OpenJS.NodeJS.LTS"
+}
+
+if (-not (Get-Command rustc -ErrorAction SilentlyContinue)) {
+  throw "Windows Rust was not found. Install it with: winget install Rustlang.Rustup"
+}
+
+$Tauri = Get-Command tauri -ErrorAction SilentlyContinue
+$CargoTauri = Get-Command cargo-tauri -ErrorAction SilentlyContinue
+
+if (-not $Tauri -and -not $CargoTauri) {
+  throw "Tauri CLI not found. Install it with: npm install -g @tauri-apps/cli (run from a normal Windows path, not \\wsl$)"
+}
+
+$env:CARGO_INCREMENTAL = "0"
+$env:CARGO_TARGET_DIR = Join-Path $env:LOCALAPPDATA "Hermes\cargo-target\gui"
+New-Item -ItemType Directory -Force -Path $env:CARGO_TARGET_DIR | Out-Null
+
+if ($Fresh) {
+  $FreshHome = Join-Path $env:LOCALAPPDATA "Hermes\fresh-install-home"
+  if ($ResetFresh -and (Test-Path $FreshHome)) {
+    Remove-Item -Recurse -Force $FreshHome
+  }
+  New-Item -ItemType Directory -Force -Path $FreshHome | Out-Null
+  $env:HERMES_HOME = $FreshHome
+  $env:HERMES_GUI_PORT = "9140"
+  $env:HERMES_GUI_FRESH = "1"
+  Write-Host "Fresh GUI mode"
+  Write-Host "  HERMES_HOME=$FreshHome"
+  Write-Host "  HERMES_GUI_PORT=$env:HERMES_GUI_PORT"
+}
+
+Push-Location $AppRoot
+try {
+  if ($Tauri) {
+    & tauri $Command
+  }
+  else {
+    & cargo tauri $Command
+  }
+}
+finally {
+  Pop-Location
+}