feat(electrobun): hierarchical state tree (Rule 58)

New files:
- project-state.types.ts: all per-project state interfaces
- project-state.svelte.ts: unified per-project state with version counter
- app-state.svelte.ts: root facade re-exporting all stores as appState.*

Rewired components (no more local $state):
- ProjectCard: reads via appState.agent.* and appState.project.tab.*
- TerminalTabs: state in appState.project.terminals.*
- FileBrowser: state in appState.project.files.*
- CommsTab: state in appState.project.comms.*
- TaskBoardTab: state in appState.project.tasks.*

All follow Rule 57 (no $derived with new objects) and Rule 58
(state tree architecture, components are pure renderers).

ui-electrobun/src/mainview/ProjectCard.svelte

@@ -8,15 +8,8 @@
   import DocsTab from './DocsTab.svelte';
   import SshTab from './SshTab.svelte';
   import StatusDot from './ui/StatusDot.svelte';
-  import {
-    startAgent, stopAgent, sendPrompt, getSession, hasSession,
-    loadLastSession,
-    type AgentStatus, type AgentMessage,
-  } from './agent-store.svelte.ts';
-  import {
-    getActiveTab, setActiveTab, isTabActivated,
-    ALL_TABS, type ProjectTab,
-  } from './project-tabs-store.svelte.ts';
+  import { appState, type AgentStatus, type AgentMessage, type ProjectTab } from './app-state.svelte.ts';
+  import { ALL_TABS } from './project-tabs-store.svelte.ts';
 
   interface Props {
     id: string;
@@ -61,9 +54,7 @@
 
   // ── Agent session (reactive from store) ──────────────────────────
   const EMPTY_MESSAGES: AgentMessage[] = [];
-  // ALL agent session state as plain getter functions — NO $derived.
-  // $derived + store getters that return new refs = infinite loops in Svelte 5.
-  function getAgentSession() { return getSession(id); }
+  function getAgentSession() { return appState.agent.getSession(id); }
   function getAgentStatus(): AgentStatus { return getAgentSession()?.status ?? 'idle'; }
   function getAgentMessages(): AgentMessage[] { return getAgentSession()?.messages ?? []; }
   function getAgentCost(): number { return getAgentSession()?.costUsd ?? 0; }
@@ -107,7 +98,7 @@
     return getAgentMessages().length > 0 ? getAgentMessages() : EMPTY_MESSAGES;
   }
 
-  // ── Clone dialog state ──────────────────────────────────────────
+  // ── Clone dialog state (needs $state for template bindings) ─────
   let showCloneDialog = $state(false);
   let cloneBranchName = $state('');
   let cloneError = $state('');
@@ -129,33 +120,31 @@
     showCloneDialog = false;
   }
 
-  // Derived from project-tabs-store for reactive reads
-  function getCurrentTab() { return getActiveTab(id); }
+  // Tab state from project state tree
+  function getCurrentTab() { return appState.project.tab.getActiveTab(id); }
 
   // ── Load last session on mount (once, not reactive) ─────────────────
   import { onMount } from 'svelte';
-  onMount(() => { loadLastSession(id); });
+  onMount(() => { appState.agent.loadLastSession(id); });
 
   function setTab(tab: ProjectTab) {
-    setActiveTab(id, tab);
+    appState.project.tab.setActiveTab(id, tab);
   }
 
   function handleSend(text: string) {
-    if (hasSession(id)) {
-      // Session exists — send follow-up prompt
-      sendPrompt(id, text).catch((err) => {
+    if (appState.agent.hasSession(id)) {
+      appState.agent.sendPrompt(id, text).catch((err) => {
         console.error('[agent.prompt] error:', err);
       });
     } else {
-      // No session — start a new agent
-      startAgent(id, provider, text, { cwd, model }).catch((err) => {
+      appState.agent.startAgent(id, provider, text, { cwd, model }).catch((err) => {
         console.error('[agent.start] error:', err);
       });
     }
   }
 
   function handleStop() {
-    stopAgent(id).catch((err) => {
+    appState.agent.stopAgent(id).catch((err) => {
       console.error('[agent.stop] error:', err);
     });
   }
@@ -373,7 +362,7 @@
         role="tabpanel"
         aria-label="Files"
       >
-        <FileBrowser {cwd} />
+        <FileBrowser {cwd} projectId={id} />
       </div>
 
     <!-- SSH tab -->
@@ -409,7 +398,7 @@
         role="tabpanel"
         aria-label="Comms"
       >
-        <CommsTab {groupId} agentId={id} />
+        <CommsTab {groupId} projectId={id} agentId={id} />
       </div>
 
     <!-- Tasks tab (kanban board) -->
@@ -421,7 +410,7 @@
         role="tabpanel"
         aria-label="Tasks"
       >
-        <TaskBoardTab {groupId} agentId={id} />
+        <TaskBoardTab {groupId} projectId={id} agentId={id} />
       </div>
   </div>
 </article>