feat(v2): add agent tree, status bar, notifications, settings dialog (Phase 5)

Agent tree visualization (SVG) with horizontal layout and bezier edges.
Global status bar with pane counts, active agents pulse, token/cost totals.
Toast notification system with auto-dismiss and agent dispatcher integration.
Settings dialog with SQLite persistence for shell, cwd, and max panes.
Keyboard shortcuts: Ctrl+W close pane, Ctrl+, open settings.

v2/src/lib/components/StatusBar/StatusBar.svelte

@@ -0,0 +1,95 @@
+<script lang="ts">
+  import { getPanes } from '../../stores/layout.svelte';
+  import { getAgentSessions } from '../../stores/agents.svelte';
+
+  let panes = $derived(getPanes());
+  let agentSessions = $derived(getAgentSessions());
+
+  let activeAgents = $derived(agentSessions.filter(s => s.status === 'running' || s.status === 'starting').length);
+  let totalCost = $derived(agentSessions.reduce((sum, s) => sum + s.costUsd, 0));
+  let totalTokens = $derived(agentSessions.reduce((sum, s) => sum + s.inputTokens + s.outputTokens, 0));
+  let terminalCount = $derived(panes.filter(p => p.type === 'terminal').length);
+  let agentCount = $derived(panes.filter(p => p.type === 'agent').length);
+</script>
+
+<div class="status-bar">
+  <div class="left">
+    <span class="item" title="Terminal panes">{terminalCount} terminals</span>
+    <span class="sep"></span>
+    <span class="item" title="Agent panes">{agentCount} agents</span>
+    {#if activeAgents > 0}
+      <span class="sep"></span>
+      <span class="item active">
+        <span class="pulse"></span>
+        {activeAgents} running
+      </span>
+    {/if}
+  </div>
+  <div class="right">
+    {#if totalTokens > 0}
+      <span class="item tokens">{totalTokens.toLocaleString()} tokens</span>
+      <span class="sep"></span>
+    {/if}
+    {#if totalCost > 0}
+      <span class="item cost">${totalCost.toFixed(4)}</span>
+      <span class="sep"></span>
+    {/if}
+    <span class="item version">BTerminal v2</span>
+  </div>
+</div>
+
+<style>
+  .status-bar {
+    grid-column: 1 / -1;
+    display: flex;
+    align-items: center;
+    justify-content: space-between;
+    height: 24px;
+    padding: 0 10px;
+    background: var(--bg-secondary);
+    border-top: 1px solid var(--border);
+    font-size: 11px;
+    color: var(--text-muted);
+    font-family: var(--font-mono);
+    user-select: none;
+  }
+
+  .left, .right {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+  }
+
+  .sep {
+    width: 1px;
+    height: 10px;
+    background: var(--border);
+  }
+
+  .item {
+    display: flex;
+    align-items: center;
+    gap: 4px;
+  }
+
+  .active {
+    color: var(--ctp-blue);
+  }
+
+  .pulse {
+    width: 6px;
+    height: 6px;
+    border-radius: 50%;
+    background: var(--ctp-blue);
+    animation: pulse 1.5s ease-in-out infinite;
+  }
+
+  @keyframes pulse {
+    0%, 100% { opacity: 1; }
+    50% { opacity: 0.3; }
+  }
+
+  .tokens { color: var(--ctp-overlay1); }
+  .cost { color: var(--ctp-yellow); }
+  .version { color: var(--ctp-overlay0); }
+</style>