fix(tui): escape the separator in the switch binding, closing the sizing leak

The loose end from 777f974, now explained. Sessions came back from a detach on
`window-size latest` instead of `manual`, and the restore primitive round-tripped
correctly in isolation, so the corruption had to be upstream of it. It was: the
snapshot was taken from state this code had already broken.

`bindSwitchKey` passed a bare `;` between the two commands it wanted in one
binding. That is a command separator to tmux's OWN parser, not an argument: it
ended the `bind-key` and executed what followed immediately. So the binding kept
only `switch-client`, and `set-window-option ... window-size latest` RAN against
every switchable session at attach time — before the sizing snapshot was taken.
Every session was therefore snapshotted as `latest` and faithfully restored to
`latest`.

Proven against real tmux both ways before fixing: a bare `;` leaves the session
on `latest` and stores a one-command binding, while `\;` leaves it `manual` and
stores both commands.

Verified end to end: 7 sessions manual before, 1 latest + 6 manual during the
attach (the attached one follows the terminal, the rest are pre-sized), no dot
padding on a switch, and all 7 back to 120x40 manual after the detach.

This also means the "follow the terminal after switching" half of 777f974 never
actually worked — it was never in the binding.

src/tui/tui-client.ts

@@ -1004,6 +1004,13 @@ export class TuiClient {
       // It is already the right size (see presizeWindow), so `latest` changes
       // nothing on arrival and costs no repaint — it matters only if the
       // terminal is resized while sitting in that session.
+      //
+      // ⚠️ The separator MUST be an escaped `\;`. A bare `;` is a command
+      // separator to tmux's own parser, so it ends the `bind-key` and RUNS
+      // what follows immediately: the binding kept only `switch-client`, and
+      // every session got `window-size latest` executed on it at attach time.
+      // That is what left sessions on `latest` after a detach, since the
+      // snapshot was then taken from already-corrupted state.
       await this.exec('tmux', [
         '-L',
         this.socket,
@@ -1014,7 +1021,7 @@ export class TuiClient {
         'switch-client',
         '-t',
         target,
-        ';',
+        '\\;',
         'set-window-option',
         '-t',
         target,