feat(ui): About dialog, Release Notes, and new-version banner

About (in the account menu) shows frontend/backend/database versions + build.
Release Notes renders per-version highlights with a commit-SHA reference; a
dismissible banner appears once after the running build's version changes and
links into the notes. Adds a reusable Modal shell and the release-notes data
(detailed v0.1.0).

frontend/src/App.tsx

@@ -27,6 +27,10 @@ import SettingsPanel from "./components/SettingsPanel";
 import OnboardingWizard from "./components/OnboardingWizard";
 import { shouldAutoOpenOnboarding } from "./lib/onboarding";
 import Toaster from "./components/Toaster";
+import About from "./components/About";
+import ReleaseNotes from "./components/ReleaseNotes";
+import VersionBanner from "./components/VersionBanner";
+import { CURRENT_VERSION } from "./lib/releaseNotes";
 
 const DEFAULT_FILTERS: FeedFilters = {
   tags: [],
@@ -65,6 +69,14 @@ export default function App() {
   const [settingsOpen, setSettingsOpen] = useState(false);
   const [wizardOpen, setWizardOpen] = useState(false);
   const [channelFilter, setChannelFilter] = useState<ChannelStatusFilter>("all");
+  const [aboutOpen, setAboutOpen] = useState(false);
+  const [notesOpen, setNotesOpen] = useState(false);
+  const [notesHighlight, setNotesHighlight] = useState<string | undefined>(undefined);
+
+  function openReleaseNotes(highlight?: string) {
+    setNotesHighlight(highlight);
+    setNotesOpen(true);
+  }
 
   function setFilters(next: FeedFilters) {
     setFiltersState(next);
@@ -158,11 +170,13 @@ export default function App() {
         page={page}
         setPage={setPage}
         onOpenSettings={() => setSettingsOpen(true)}
+        onOpenAbout={() => setAboutOpen(true)}
         onGoToFullHistory={() => {
           setChannelFilter("needs_full");
           setPage("channels");
         }}
       />
+      <VersionBanner onOpen={() => openReleaseNotes(CURRENT_VERSION)} />
       <div className="flex flex-1 min-h-0">
         {page === "feed" && (
           <Sidebar
@@ -213,6 +227,18 @@ export default function App() {
       {wizardOpen && meQuery.data && (
         <OnboardingWizard me={meQuery.data} onClose={() => setWizardOpen(false)} />
       )}
+      {aboutOpen && (
+        <About
+          onClose={() => setAboutOpen(false)}
+          onOpenReleaseNotes={() => {
+            setAboutOpen(false);
+            openReleaseNotes();
+          }}
+        />
+      )}
+      {notesOpen && (
+        <ReleaseNotes onClose={() => setNotesOpen(false)} highlight={notesHighlight} />
+      )}
       <Toaster />
     </div>
   );