fix(terminal): merge-time fixes for the silent-failure paths (#431)

- While another device holds the pane width (_paneWidthRefused), a resize
  now asks for the container's width without applying it locally
  (_geometryForResizeRequest: rows follow the container, columns stay at
  the PTY's). Fitting first re-wrapped the whole buffer to the container
  and back on every 30s mobile retry, and throttledResize ran the
  scrollback clear for a resize that brings no redraw. selectSession
  clears the flag, since it belongs to the previous pane. New unit tests
  run the real mixin against a fake terminal and fail without the fix.
- Session seeds _ptyCols/_ptyRows at spawn (_notePtySpawnGeometry), so a
  reattached pane reports its tmux window's real size through ptyGeometry.
- Session.resize's declined-branch comment names ptyGeometry, not the
  deleted ptyCols/ptyRows getters.
- Delete the dead terminalGeometryAgrees() and its window export.
- test/xterm-private-api.test.ts header: it pins the exact locked version,
  so any bump fails, not only a major.
- The main-terminal fit sweep also matches fitAddon?.fit?.(), and
  CLAUDE.md names the modules it actually covers.

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

src/web/public/constants.js

@@ -1770,11 +1770,6 @@ function clampTerminalDimensions(proposed) {
   };
 }
 
-/** Whether two geometries are the same screen. Either being absent is a mismatch. */
-function terminalGeometryAgrees(a, b) {
-  return !!a && !!b && a.cols === b.cols && a.rows === b.rows;
-}
-
 /**
  * What to do when the server reports the PTY's real geometry.
  *
@@ -1829,7 +1824,6 @@ if (typeof window !== 'undefined') {
   };
   window.CodemanTerminalGeometry = {
     clampTerminalDimensions,
-    terminalGeometryAgrees,
     reconcilePtyGeometry,
     TERMINAL_MIN_COLS,
     TERMINAL_MIN_ROWS,