feat: add auto-memory panel, /memory command, and unified toast system

- Add /memory CLI built-in slash command
- Refactor MemoryBrowserPanel to accept isOpen/onClose props
- Add Send /memory and Refresh buttons to MemoryBrowserPanel header
- Add Memory Manager entry to NavMenu
- Create unified ToastContainer replacing AchievementNotification and
  UpdateNotification with a single stacked toast system
- Add toasts store with info (4s), achievement (5s), and persistent
  update toast types
- Move getAchievementRarity and getRarityColour helpers to toasts store
- Detect auto-memory writes in tauri.ts output listener and fire toast
- Remove action buttons from update toast; version is now a direct link

Closes #212

src/lib/components/NavMenu.svelte

@@ -24,6 +24,7 @@
   import ChangelogPanel from "./ChangelogPanel.svelte";
   import TaskLoopPanel from "./TaskLoopPanel.svelte";
   import WorkflowPanel from "./WorkflowPanel.svelte";
+  import MemoryBrowserPanel from "./MemoryBrowserPanel.svelte";
   import { injectTextStore } from "$lib/stores/projectContext";
 
   const DISCORD_URL = "https://chat.nhcarrigan.com";
@@ -69,6 +70,7 @@
   let showChangelog = $state(false);
   let showTaskLoop = $state(false);
   let showWorkflowPanel = $state(false);
+  let showMemoryPanel = $state(false);
 
   const progress = $derived($achievementProgress);
   const activeAgentCount = $derived($runningAgentCount);
@@ -176,6 +178,19 @@
       <span>Session History</span>
     </button>
 
+    <!-- Memory Manager -->
+    <button onclick={menuAction(() => (showMemoryPanel = true))} class="nav-item">
+      <svg class="w-5 h-5 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24">
+        <path
+          stroke-linecap="round"
+          stroke-linejoin="round"
+          stroke-width="2"
+          d="M9.663 17h4.673M12 3v1m6.364 1.636l-.707.707M21 12h-1M4 12H3m3.343-5.657l-.707-.707m2.828 9.9a5 5 0 117.072 0l-.548.547A3.374 3.374 0 0014 18.469V19a2 2 0 11-4 0v-.531c0-.895-.356-1.754-.988-2.386l-.548-.547z"
+        />
+      </svg>
+      <span>Memory Manager</span>
+    </button>
+
     <!-- To-Do List -->
     <button onclick={menuAction(() => (showTodoPanel = true))} class="nav-item">
       <svg class="w-5 h-5 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24">
@@ -547,6 +562,10 @@
   />
 {/if}
 
+{#if showMemoryPanel}
+  <MemoryBrowserPanel isOpen={showMemoryPanel} onClose={() => (showMemoryPanel = false)} />
+{/if}
+
 {#if showWorkflowPanel}
   <WorkflowPanel
     onClose={() => (showWorkflowPanel = false)}