fix: drop the two keymap and style entries nothing reaches

`mark()` had no callers (knip's only finding on this branch), and the
renderer's fallback help list advertised `r` resume, which is deferred
with the rest of phase 3: a help screen naming a verb the build does not
implement is worse than no help.

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

src/tui/tui-render.ts

@@ -675,7 +675,6 @@ function helpLines(glyphs: TuiGlyphSet, custom?: ReadonlyArray<readonly [string,
     ['x', 'kill (typed confirmation)'],
     ['/', 'search'],
     ['g', 'away digest'],
-    ['r', 'resume a recent session'],
     ['?', 'this help'],
     ['q', 'quit'],
   ];