fix(terminal): merge-time fixes for #494

- Skip and latch a bounded Shell window once the browser is at xterm's
  scrollback cap (scrollback + rows): a 1 MiB window of short lines can carry
  more rows than the browser can ever hold, so it replayed and re-captured on
  every scroll-to-top with no 60 s back-off.
- Label a replayed bounded window 'tail' even when the capture was byte-capped,
  so the banner keeps offering Load full history instead of calling the rest
  unrecoverable.
- Pin GET /terminal?full=1&tail=<n> in the route tests: full-history source,
  truncationReason 'tail', and the closing relative cursor move survive the cut.
- Log the bounded skip via _logScrollRouting('repull-skipped-bounded').

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/terminal-scroll-routing.test.ts

@@ -114,7 +114,7 @@ describe('full-history re-pull downgrade guard (issue #205 round 2)', () => {
     // Also anchored on the open paren: the guard is handed the rows the caller
     // already estimated, and this test is about ORDER, not the argument list.
     const guard = source.indexOf('this._replayWouldShrinkBuffer(buffer', start);
-    const boundedSkip = source.indexOf('boundedShellPull && windowRows <=', start);
+    const boundedSkip = source.indexOf('boundedShellPull && (windowRows <= rowsNow || browserFull)', start);
     const reset = source.indexOf('this._resetTerminalForReplay()', start);
 
     expect(start).toBeGreaterThan(-1);