perf(frontend): keep the changelog out of the eager App chunk (C-3.19)

App.tsx imported CURRENT_VERSION from releaseNotes, which pulled its ~900-line
changelog into the eager App chunk and defeated the lazy ReleaseNotes split. App now
uses FRONTEND_VERSION (the built VITE_APP_VERSION, equal to RELEASE_NOTES[0].version
by release convention) from lib/version, and CURRENT_VERSION is removed. Verified in
the built bundle: the changelog text now lives only in the ReleaseNotes lazy chunk.

frontend/src/lib/releaseNotes.ts

@@ -923,5 +923,3 @@ export const RELEASE_NOTES: ReleaseEntry[] = [
     ],
   },
 ];
-
-export const CURRENT_VERSION = RELEASE_NOTES[0]?.version ?? "dev";