Multi-account GitHub auth + UI polish (model logos, markdown, scroll behavior) (#219)

* feat: display provider logos for favorite/recent models

Show provider logo next to model name in favorites and recents
Render provider logos in ModelControls, ModelMultiSelect, and ModelSelector lists
Maintain zero-logo state for other sections to avoid clutter

* feat: render user message as markdown instead of plain text

Render agent mentions as markdown links in user text
Apply inside list style for chat content to fix list rendering
Rely on SimpleMarkdownRenderer for consistent rendering

* fix(openchamber): adjust layout and overscroll behavior

Enable overscroll-auto on overlay containers for smoother scrolling
Move page content to full-width wrapper and preserve section borders
Show AboutSettings inside its own bordered block when visible

* feat: integrate GitHub auth status store and UI

Introduce GitHubAuthStore to track connection status and polling
Show GitHub avatar in header when connected
Guard issue/pr dialogs behind GitHub auth status and show notices

* feat: add GitHub multi-account support

Add API and UI flow to activate a GitHub account
Show and switch between multiple GitHub accounts in header
Persist and normalize accounts list with current selection

packages/web/src/api/github.ts

@@ -67,6 +67,19 @@ export const createWebGitHubAPI = (): GitHubAPI => ({
     return { removed: Boolean(payload?.removed) };
   },
 
+  async authActivate(accountId: string): Promise<GitHubAuthStatus> {
+    const response = await fetch('/api/github/auth/activate', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json', Accept: 'application/json' },
+      body: JSON.stringify({ accountId }),
+    });
+    const payload = await jsonOrNull<GitHubAuthStatus & { error?: string }>(response);
+    if (!response.ok || !payload) {
+      throw new Error(payload?.error || response.statusText || 'Failed to activate GitHub account');
+    }
+    return payload;
+  },
+
   async me(): Promise<GitHubUserSummary> {
     const response = await fetch('/api/github/me', { method: 'GET', headers: { Accept: 'application/json' } });
     const payload = await jsonOrNull<GitHubUserSummary & { error?: string }>(response);