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/styles.css

@@ -0,0 +1,51 @@
+/*
+ * Hermes Setup — defer entirely to the desktop's styles.css.
+ *
+ * Rather than re-implement the Hermes design system (and inevitably drift
+ * from it), we import apps/desktop/src/styles.css wholesale. The desktop
+ * is the canonical source of truth for fonts, color tokens, button chrome,
+ * scrollbars, layout utilities, and animations. Any change to the
+ * Hermes look propagates here automatically with no copy-paste maintenance.
+ *
+ * Path resolution caveats:
+ *   - Tailwind v4's `@import` resolves relative to this file. The desktop's
+ *     `@source '../../../node_modules/...'` declarations therefore re-resolve
+ *     against apps/bootstrap-installer/src/. Since both apps live two levels
+ *     deep under the same repo root, `../../../node_modules` lands in the
+ *     same place. (Verify if either app ever moves.)
+ *   - The desktop's `@font-face url('../../../node_modules/...')` references
+ *     are baked into the *imported* stylesheet; CSS resolves url()s relative
+ *     to the file that contains them, so they continue to point at the
+ *     correct node_modules path even from here.
+ *
+ * Forced light mode: the desktop ships with a runtime theme switcher
+ * (ThemeProvider + applyTheme) that can flip to dark via document.documentElement.
+ * The installer has no UI for theme switching, so we stay on the desktop's
+ * default light surface (Nous-blue accent on near-white chrome).
+ */
+@import '../../desktop/src/styles.css';
+
+/* Installer-only additions: a fade-in animation and a warm radial glow
+   for the welcome screen. Everything else inherits from the desktop. */
+@keyframes hermes-fade-in {
+  from {
+    opacity: 0;
+    transform: translateY(4px);
+  }
+  to {
+    opacity: 1;
+    transform: translateY(0);
+  }
+}
+
+.hermes-fade-in {
+  animation: hermes-fade-in 0.45s ease-out both;
+}
+
+.hermes-glow {
+  background: radial-gradient(
+    ellipse at center,
+    color-mix(in srgb, var(--ui-warm) 18%, transparent) 0%,
+    transparent 60%
+  );
+}