feat(electrobun): fixes + 7 new features (terminal input, file browser, memory, toasts)

Fixes:
- Terminal accepts keyboard input (echo mode with prompt)
- Terminal drawer collapses properly (display:none preserves xterm state)

Features:
- 6 project tabs: Model | Docs | Context | Files | SSH | Memory
- FileBrowser.svelte: recursive tree with expand/collapse + file preview
- MemoryTab.svelte: memory cards with trust badges (human/agent/auto)
- Subagent tree in AgentPane (demo: search-agent, test-runner)
- Drag resize handle between agent pane and terminal
- Theme dropdown in Settings (4 Catppuccin flavors)
- ToastContainer.svelte: auto-dismiss notifications

ui-electrobun/src/mainview/App.svelte

@@ -2,6 +2,7 @@
   import ProjectCard from './ProjectCard.svelte';
   import SettingsDrawer from './SettingsDrawer.svelte';
   import CommandPalette from './CommandPalette.svelte';
+  import ToastContainer from './ToastContainer.svelte';
 
   // ── Types ─────────────────────────────────────────────────────
   type AgentStatus = 'running' | 'idle' | 'stalled';
@@ -140,6 +141,7 @@
 
 <SettingsDrawer open={settingsOpen} onClose={() => settingsOpen = false} />
 <CommandPalette open={paletteOpen} onClose={() => paletteOpen = false} />
+<ToastContainer />
 
 <div class="app-shell">
   <!-- Sidebar icon rail -->