feat: center hints over the timeline + add hubris footer

- KeyboardHints: switch from fixed positioning to absolute, mounted
  inside the main content column. The column is now relative-positioned
  so the hints overlay centers against the timeline area instead of the
  raw viewport (which was off-center because of the sidebars).
- AppFooter: tiny "Built with hubris • <YEAR in roman>" pinned to the
  bottom-right corner of the main column. Year is computed at render
  time and converted via a small toRoman helper.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/App.tsx

@@ -6,6 +6,7 @@ import { TopBar } from './components/layout/TopBar'
 import { ScanProgress } from './components/ScanProgress'
 import { ToastContainer } from './components/ToastContainer'
 import { KeyboardHints } from './components/KeyboardHints'
+import { AppFooter } from './components/AppFooter'
 import { PreviewView } from './components/preview/PreviewView'
 import { FilterBar } from './components/filter/FilterBar'
 import { DiscardActionBar } from './components/discard/DiscardActionBar'
@@ -66,13 +67,19 @@ function App() {
 
         {/* Main column — filter bar, discard bar, timeline. Lives to the
          *  right of the left sidebar so the filter row doesn't bleed
-         *  across the sidebar. */}
-        <div className="flex min-w-0 flex-1 flex-col">
+         *  across the sidebar. relative so the KeyboardHints overlay
+         *  centers against this column, not the viewport. */}
+        <div className="relative flex min-w-0 flex-1 flex-col">
           <FilterBar />
           <DiscardActionBar />
           <div className="flex-1 overflow-auto">
             <Timeline />
           </div>
+          {/* Floating keyboard hints — bottom-center of the main column,
+           *  glassy. Mounted here so it's centered against the timeline,
+           *  not the viewport (which would be offset by the sidebars). */}
+          <KeyboardHints />
+          <AppFooter />
         </div>
 
         {/* Right Sidebar */}
@@ -85,10 +92,6 @@ function App() {
         </div>
       </div>
 
-      {/* Floating keyboard hints — pinned bottom-center, glassy. Sits
-       *  above the timeline and below the toast layer. */}
-      <KeyboardHints />
-
       {/* Scan Progress Indicator */}
       <ScanProgress />