feat(v3): implement Mission Control MVP (Phases 1-5)

Phase 1: Data model - groups.rs (Rust structs + load/save groups.json),
groups.ts (TypeScript interfaces), groups-bridge.ts (IPC adapter),
workspace.svelte.ts (replaces layout store), SQLite migrations
(agent_messages, project_agent_state tables, project_id column),
--group CLI argument.

Phase 2: Project shell layout - GlobalTabBar, ProjectGrid, ProjectBox,
ProjectHeader, CommandPalette, DocsTab, ContextTab, SettingsTab,
App.svelte full rewrite (no sidebar/TilingGrid).

Phase 3: ClaudeSession.svelte wrapping AgentPane per-project.
Phase 4: TerminalTabs.svelte with shell/SSH/agent tab types.
Phase 5: TeamAgentsPanel + AgentCard for compact subagent view.

Also fixes AgentPane Svelte 5 event modifier (on:click -> onclick).

v2/src/lib/components/Workspace/ProjectGrid.svelte

@@ -0,0 +1,85 @@
+<script lang="ts">
+  import { onMount, onDestroy } from 'svelte';
+  import { getEnabledProjects, getActiveProjectId, setActiveProject } from '../../stores/workspace.svelte';
+  import ProjectBox from './ProjectBox.svelte';
+
+  let containerEl: HTMLDivElement | undefined = $state();
+  let containerWidth = $state(0);
+
+  let projects = $derived(getEnabledProjects());
+  let activeProjectId = $derived(getActiveProjectId());
+  let visibleCount = $derived(
+    Math.min(projects.length, Math.max(1, Math.floor(containerWidth / 520))),
+  );
+
+  let observer: ResizeObserver | undefined;
+
+  onMount(() => {
+    if (containerEl) {
+      containerWidth = containerEl.clientWidth;
+      observer = new ResizeObserver(entries => {
+        for (const entry of entries) {
+          containerWidth = entry.contentRect.width;
+        }
+      });
+      observer.observe(containerEl);
+    }
+  });
+
+  onDestroy(() => {
+    observer?.disconnect();
+  });
+</script>
+
+<div
+  class="project-grid"
+  bind:this={containerEl}
+  style="--visible-count: {visibleCount}"
+>
+  {#each projects as project, i (project.id)}
+    <div class="project-slot">
+      <ProjectBox
+        {project}
+        slotIndex={i}
+        active={activeProjectId === project.id}
+        onactivate={() => setActiveProject(project.id)}
+      />
+    </div>
+  {/each}
+
+  {#if projects.length === 0}
+    <div class="empty-state">
+      No enabled projects in this group. Go to Settings to add projects.
+    </div>
+  {/if}
+</div>
+
+<style>
+  .project-grid {
+    display: flex;
+    gap: 4px;
+    height: 100%;
+    overflow-x: auto;
+    scroll-snap-type: x mandatory;
+    padding: 4px;
+  }
+
+  .project-slot {
+    flex: 0 0 calc((100% - (var(--visible-count) - 1) * 4px) / var(--visible-count));
+    min-width: 480px;
+    display: flex;
+  }
+
+  .project-slot > :global(*) {
+    flex: 1;
+  }
+
+  .empty-state {
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    width: 100%;
+    color: var(--ctp-overlay0);
+    font-size: 0.9rem;
+  }
+</style>