docs(split): comments say what TerminalTile does now

The rename from SplitTerminalPane carried comments over that the PR 1
changes made untrue:

- constants.js buildSplitPickerSessions said TerminalTile._sendResize has
  no detached check (it stands aside like the primary pane) and that Pane
  B sends no `seq` (its input rides the exactly-once queue). The
  conclusions stay: a detached session's window owns its PTY size, and a
  session with no PTY has a pane nothing feeds or reads.
- terminal-split.js said TerminalTile has no "dims unchanged" skip (it has
  _lastSentDims), and its @loadorder still ended at respawn-ui.js rather
  than tile-grid.js.
- terminal-tile.js still called every pane "Pane B", said a shell load
  lands in "a 50000-line xterm" (the scrollback is an option now) and
  that a TUI session always gets a full replay (with boundedLoad, grid
  tiles get the bounded window), and told some reasons as history ("an earlier draft", "used
  to", "It LOOKED intermittent"). Those now give the reason in the
  present tense, and the comments touched lose their em dashes.
  writeChunked's doc comment is left as it is: the perf work rewrites
  that function and owns its comment.

Comments only.

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

src/web/public/terminal-split.js

@@ -8,7 +8,7 @@
  *
  * @dependency terminal-tile.js (window.TerminalTile)
  * @dependency constants.js (window.CodemanSplitPane, SPLIT_PANE_MIN_WIDTH)
- * @loadorder 7.5 of 16, loaded after terminal-tile.js and before respawn-ui.js
+ * @loadorder 7.5 of 16, loaded after terminal-tile.js and before tile-grid.js
  */
 
 Object.assign(CodemanApp.prototype, {
@@ -281,10 +281,9 @@ Object.assign(CodemanApp.prototype, {
     // frame). Coalesced to one call per animation frame below — a raw
     // mousemove stream fires far faster than the browser repaints, and
     // without the rAF gate each event did a full xterm reflow on BOTH
-    // panes AND sent Pane B a `{t:'z'}` resize frame (TerminalTile has
-    // no client-side "dims unchanged" skip), which fanned out into a
-    // `tmux resize-window` child plus a SIGWINCH per frame — roughly fifty
-    // of each dragging across half a wide viewport.
+    // panes AND sent Pane B a `{t:'z'}` resize frame, which fanned out
+    // into a `tmux resize-window` child plus a SIGWINCH per frame, roughly
+    // fifty of each dragging across half a wide viewport.
     const applyDragPercent = (clientX) => {
       const container = divider.parentElement;
       // The split can auto-collapse mid-drag (the other pane's session