feat(v2): scaffold Tauri 2.x + Svelte 5 project (Phase 1)

- Tauri 2.10 + Svelte 5.45 + TypeScript + Vite 7
- Catppuccin Mocha theme with CSS variables and semantic aliases
- CSS Grid layout: sidebar (260px) + workspace, responsive breakpoints
  for ultrawide (3440px+) and narrow (<1200px)
- Component structure: Layout/, Terminal/, Agent/, Markdown/, Sidebar/
- Svelte 5 stores with $state runes: sessions, agents, layout
- SDK message adapter (abstracts Agent SDK wire format)
- PTY bridge (Tauri IPC wrapper, stubbed for Phase 2)
- Node.js sidecar entry point (stdio NDJSON, stubbed for Phase 3)
- Rust modules: pty, sidecar, watcher, session (stubbed)
- Vite dev server on port 9700
- Build verified: binary + .deb + .rpm + AppImage all produced

v2/src/lib/stores/layout.ts

@@ -0,0 +1,28 @@
+// Layout state management — Svelte 5 runes
+// Phase 2: pane positions, resize, presets
+
+export type LayoutPreset = '1-col' | '2-col' | '3-col' | '2x2' | 'master-stack';
+
+export interface PaneState {
+  id: string;
+  sessionId: string;
+  row: number;
+  col: number;
+  rowSpan: number;
+  colSpan: number;
+}
+
+let activePreset = $state<LayoutPreset>('1-col');
+let panes = $state<PaneState[]>([]);
+
+export function getActivePreset() {
+  return activePreset;
+}
+
+export function setPreset(preset: LayoutPreset) {
+  activePreset = preset;
+}
+
+export function getPanes() {
+  return panes;
+}