Add Nebula Shell v0 prototype and redesign

Introduce a working v0 Nebula Shell prototype (Tauri frontend) and redesign docs. Adds a complete frontend under src/ (views: home, lock, library, settings, overlays), core adapters (input, nav, passkey, router, state), global styles and shell guidelines, and view-specific HTML/CSS/JS. Update README with prototype notes, install/run/build instructions and controller testing tips. Update package.json to add dev/build scripts and add @nebulaproject/core as a dependency. Also include a detailed REDESIGN_DOCUMENTATION.md describing the Xbox-inspired horizontal dashboard, component patterns, and developer notes.

src/styles/shell-guidelines.md

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+# Nebula Shell UI Guidelines (Dashboard Refresh)
+
+## Layout Structure
+- Home uses a left-aligned horizontal tile rail (`.tile-rail`) with one primary row of large app tiles.
+- Top bar is shared across shell views with brand left and time/profile right.
+- Settings uses a horizontal category bar at top and card panel content below.
+- Lock screen keeps immersive centered time/date and reveals PIN panel on first input.
+
+## Animation Guidelines
+- Use cubic-bezier curves only:
+  - `--nebula-ease-console`: focus travel and panel transitions.
+  - `--nebula-ease-standard`: opacity and ambient motion.
+  - `--nebula-ease-snap`: press pulse feedback.
+- Focus transitions target `120ms–180ms` (`--nebula-duration-fast` / `--nebula-duration-nav`).
+- Use transform/opacity for movement and avoid layout-triggering transitions.
+- Page changes use `.view` to `.view-entered` slide-in transitions.
+- Press feedback uses `.is-pressed` and `uiPressPulse` keyframes.
+
+## Component Breakdown
+
+### TopBar
+- Class roots: `.shell-topbar`, `.shell-brand`, `.shell-status`, `.shell-time`, `.shell-avatar`, `.shell-accent-line`.
+- Purpose: persistent identity + status + navigation-reactive accent line.
+- Reactive token: `--nebula-accent-line-x` updates from focus manager.
+
+### TileRow
+- Class root: `.tile-rail`.
+- Purpose: horizontal app rail with controller-first left/right travel and smooth scroll.
+- Behavior: focus auto-centers via `scrollTo` and updates parallax variables.
+
+### Tile
+- Class roots: `.tile`, `.dashboard-tile`, `.tile-icon`, `.tile-label`, `.tile-meta`.
+- Focus state: `.is-focused` scales tile and adds cyan glow outline.
+- Press state: `.is-pressed` triggers pulse animation and hook events.
+
+### BackgroundLayer
+- DOM root: `#nebula-background` with `.nebula-layer` children (`gradient`, `starfield`, `fog`, `vignette`).
+- Purpose: animated nebula depth stack with subtle star motion and fog drift.
+- Parallax token: `--bg-parallax-x` supports focus-driven depth shift.
+
+### FocusManager
+- Implementation root: `src/core/nav.js`.
+- Responsibilities:
+  - Maintain focused element and directional navigation.
+  - Apply `.is-focused` state and `aria-selected`.
+  - Publish focus telemetry events (`nebula-focus-change`).
+  - Update CSS vars (`--nebula-accent-line-x`, `--nebula-focus-strength`).
+
+## UI Hook Contract (No Audio Implementation)
+- `window` `CustomEvent("nebula-ui-hook")` details:
+  - `type: "focus" | "move" | "accept" | "back"`
+  - Optional metadata (`target`, `action`, `focusKey`)
+- Intended use: external UI audio/haptics bridge without coupling shell visuals to playback.