feat(jamguide): Knowledge Center shell — four-section dock with level filter (task L-22)

Jam Guide (live, verbatim Roadmap move) / Explore (KB browser + famous
progressions, filter-exempt) / Voicings (picker follows live chord ->
VoicingBrowser) / Licks & Techniques (LickCard grids + one legend,
honest empty states). Shared foundation/intermediate filter chips;
ExplorePanel refactored to named exports (was orphaned, now imported).
App.jsx: exactly one additive prop (onChordClick). Critic PASS (48/48
SSR checks; audio contract grep clean; Roadmap hunks byte-identical).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/App.jsx

@@ -675,6 +675,7 @@ export default function App() {
         bpm={bpm}
         currentChord={currentChord}
         onFocusChord={setJamFocusChord}
+        onChordClick={setSelectedChord}
       />
     </div>
   )