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/Agent/AgentPane.svelte

@@ -302,7 +302,7 @@
                 <button
                   class="skill-item"
                   class:active={i === skillMenuIndex}
-                  onmousedown|preventDefault={() => handleSkillSelect(skill)}
+                  onmousedown={(e) => { e.preventDefault(); handleSkillSelect(skill); }}
                 >
                   <span class="skill-name">/{skill.name}</span>
                   <span class="skill-desc">{skill.description}</span>