feat(installer): Tauri bootstrap installer for first-time onboarding

Hermes-Setup.exe is a small signed Rust+Tauri binary that drives
scripts/install.ps1 stage-by-stage with a native UI matching the
desktop's design language. Replaces the chicken-and-egg pattern of
shipping a 200MB Electron app whose first launch existed only to
run install.ps1.

The architecture:

  Rust backend (src-tauri/):
    bootstrap.rs        orchestrator -- Tauri commands, stage iteration
    install_script.rs   resolve install.ps1 (dev checkout, cache, GitHub raw)
    powershell.rs       spawn powershell, line-stream stdout/stderr, parse JSON
    events.rs           BootstrapEvent types -- mirror bootstrap-runner.cjs
    paths.rs            HERMES_HOME resolution + tracing log setup
    build.rs            bakes BUILD_PIN_COMMIT / BUILD_PIN_BRANCH from
                        'git rev-parse HEAD' at compile time

  React frontend (src/):
    Tauri webview rendering 4 screens (welcome / progress / success /
    failure), driven by nanostores subscribing to the Rust event stream.
    Visual layer reuses the desktop's styles.css wholesale via @import
    so the installer and desktop never drift visually.

  Distribution:
    targets = ['app', 'dmg', 'appimage'] -- no NSIS/MSI wrapper. The
    raw target/release/Hermes-Setup.exe IS the artifact on Windows;
    .dmg + .app on macOS; AppImage on Linux. One file, double-click,
    no installer-installing-an-installer pattern.

  Compile-time pinning:
    build.rs reads 'git rev-parse HEAD' and emits
    cargo:rustc-env=BUILD_PIN_COMMIT=<sha> + BUILD_PIN_BRANCH=<branch>.
    bootstrap.rs's option_env!() picks these up so the binary fetches
    install.ps1 from the exact SHA it was tested against. CI / release
    builds can override via HERMES_BUILD_PIN_COMMIT env var.

  Windows manifest:
    hermes-setup.manifest declares level='asInvoker' so the
    productName 'Hermes Setup' doesn't trip Windows's installer-
    detection heuristic and refuse to launch without elevation.
    Also declares PerMonitorV2 DPI + UTF-8 active code page + Common
    Controls v6.

Limitations of this initial version:

  * No code signing -- Windows SmartScreen will warn once on Hermes-Setup.exe
    ('More info -> Run anyway'). The downstream binaries it produces
    (Hermes.exe in win-unpacked/, the hermes CLI) are locally-built and
    therefore don't carry MOTW, so they launch without SmartScreen
    intervention. Cert procurement tracked separately.

  * macOS and Linux build paths defined but untested -- Windows-only V1.

apps/bootstrap-installer/src-tauri/src/lib.rs

@@ -0,0 +1,66 @@
+//! Hermes Setup — Tauri entrypoint.
+//!
+//! Spawns a single window pointed at the React frontend (apps/bootstrap-installer/src/).
+//! All install-time work lives in `bootstrap.rs` and is invoked through the Tauri
+//! commands registered at the bottom of `run()`.
+//!
+//! The Windows-subsystem strip lives on the binary crate (src/main.rs), not
+//! here — a crate-level attribute on a lib doesn't propagate to the linker
+//! flags of the executable that consumes it.
+
+mod bootstrap;
+mod events;
+mod install_script;
+mod powershell;
+mod paths;
+
+use std::sync::Arc;
+use tokio::sync::Mutex;
+
+/// Process-wide install state, shared across Tauri commands.
+///
+/// The bootstrap is a one-shot, single-tenant process — we only need one
+/// of these per window. `Arc<Mutex<...>>` lets command handlers grab it
+/// without lifetime gymnastics.
+pub struct AppState {
+    pub bootstrap: Mutex<Option<bootstrap::BootstrapHandle>>,
+}
+
+impl Default for AppState {
+    fn default() -> Self {
+        Self {
+            bootstrap: Mutex::new(None),
+        }
+    }
+}
+
+#[cfg_attr(mobile, tauri::mobile_entry_point)]
+pub fn run() {
+    // Tracing → bootstrap-installer.log under HERMES_HOME/logs/ so install
+    // failures leave a trail for support. Console output also goes here in
+    // debug builds.
+    let _guard = paths::init_logging();
+
+    tracing::info!("Hermes Setup starting");
+
+    tauri::Builder::default()
+        .plugin(tauri_plugin_dialog::init())
+        .plugin(tauri_plugin_opener::init())
+        .plugin(tauri_plugin_process::init())
+        .plugin(tauri_plugin_shell::init())
+        .manage(Arc::new(AppState::default()))
+        .invoke_handler(tauri::generate_handler![
+            // Bootstrap lifecycle
+            bootstrap::start_bootstrap,
+            bootstrap::cancel_bootstrap,
+            bootstrap::get_bootstrap_status,
+            // Hand-off
+            bootstrap::launch_hermes_desktop,
+            // Diagnostics
+            paths::get_log_path,
+            paths::get_hermes_home,
+            paths::open_log_dir,
+        ])
+        .run(tauri::generate_context!())
+        .expect("error while running Hermes Setup");
+}