feat: changelog panel with runtime release fetching

Adds a Changelog panel accessible from the nav menu. Fetches all
releases from the Gitea API on open and renders each entry with
version badge, date, pre-release tag, and markdown release notes.
Highlights the currently installed version with a pink "current" badge.

src/lib/components/NavMenu.svelte

@@ -21,6 +21,7 @@
   import McpManagementPanel from "./McpManagementPanel.svelte";
   import ProjectContextPanel from "./ProjectContextPanel.svelte";
   import PrdPanel from "./PrdPanel.svelte";
+  import ChangelogPanel from "./ChangelogPanel.svelte";
   import { injectTextStore } from "$lib/stores/projectContext";
 
   const DISCORD_URL = "https://chat.nhcarrigan.com";
@@ -63,6 +64,7 @@
   let showMcpPanel = $state(false);
   let showProjectContext = $state(false);
   let showPrdPanel = $state(false);
+  let showChangelog = $state(false);
 
   const progress = $derived($achievementProgress);
   const activeAgentCount = $derived($runningAgentCount);
@@ -346,6 +348,19 @@
       <span>Support Us</span>
     </button>
 
+    <!-- Changelog -->
+    <button onclick={menuAction(() => (showChangelog = 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 5H7a2 2 0 00-2 2v12a2 2 0 002 2h10a2 2 0 002-2V7a2 2 0 00-2-2h-2M9 5a2 2 0 002 2h2a2 2 0 002-2M9 5a2 2 0 012-2h2a2 2 0 012 2M9 12h6M9 16h4"
+        />
+      </svg>
+      <span>Changelog</span>
+    </button>
+
     <!-- About -->
     <button onclick={menuAction(() => (showAbout = true))} class="nav-item">
       <svg class="w-5 h-5 shrink-0" fill="none" stroke="currentColor" viewBox="0 0 24 24">
@@ -475,6 +490,10 @@
   />
 {/if}
 
+{#if showChangelog}
+  <ChangelogPanel onClose={() => (showChangelog = false)} />
+{/if}
+
 <style>
   .nav-item {
     display: flex;