chore: drop static shortcut drawer; inline contextual hints

The bottom-left KeyboardShortcuts drawer duplicated information that
the contextual KeyboardHints pill already shows for the current
selection state. Removing it in favor of the contextual hints alone.

KeyboardHints was previously a fixed top-14 overlay, which collided
with the FilterBar when it was opened — the hints panel covered the
filter controls. Refactored it to render inline in the App header
stack (TopBar / FilterBar / ActiveFilterChips / KeyboardHints /
Timeline) so it flows naturally and never overlaps.

Also:
- Hide hints in loupe mode (the loupe has its own context)
- Replace the deleted shortcuts (Ctrl+A, Trash) with the newly wired
  ones (\\ Filters, / Search, E Loupe) so the hints surface them

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

frontend/src/App.tsx

@@ -6,7 +6,6 @@ import { RightSidebar } from './components/layout/RightSidebar'
 import { TopBar } from './components/layout/TopBar'
 import { ScanProgress } from './components/ScanProgress'
 import { ToastContainer } from './components/ToastContainer'
-import { KeyboardShortcuts } from './components/KeyboardShortcuts'
 import { KeyboardHints } from './components/KeyboardHints'
 import { LoupeView } from './components/loupe/LoupeView'
 import { FilterBar } from './components/filter/FilterBar'
@@ -53,6 +52,7 @@ function App() {
       <TopBar />
       <FilterBar />
       <ActiveFilterChips />
+      <KeyboardHints />
 
       <div className="flex flex-1 overflow-hidden">
         {/* Left Sidebar */}
@@ -79,12 +79,6 @@ function App() {
         </div>
       </div>
 
-      {/* Contextual Keyboard Hints */}
-      <KeyboardHints />
-
-      {/* Keyboard Shortcuts Legend */}
-      <KeyboardShortcuts />
-
       {/* Scan Progress Indicator */}
       <ScanProgress />