Pure move and rename, no behavior change. The split pane's second
terminal (SplitTerminalPane) moves out of terminal-split.js into its own
terminal-tile.js (load order 7.4) as TerminalTile, so the tile grid can
reuse it. terminal-split.js keeps the split orchestration (picker,
divider, auto-collapse) and constructs a TerminalTile for Pane B.
Tests follow the class: split-pane-terminal-unit becomes
terminal-tile-unit, and the Shift+Enter guard and the two browser suites
read terminal-tile.js / window.TerminalTile. The browser suites match
master (one pre-existing environmental failure in both).
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
