fix(tui): say alt+1-9 on the bar, and stop the dot grid when switching

The bar now reads "alt+1-9 switch · F1 back to the codeman dashboard", so the
switch keys are discoverable instead of secret. Shown only when those keys were
actually claimed, the same rule the way-out key follows: a bar naming a key
that does nothing is the bug this series started with.

THE DOT GRID. Switching landed in a pane occupying part of the terminal with
tmux's dot fill everywhere else. It was never a size mismatch — the window was
already the right size. `window-size latest` only resizes a window while a
client is ON it, and the sessions behind the tab strip have none until you
switch, so the resize happened AT the switch: tmux painted the newly-available
area with dots and an idle claude had no reason to redraw into it. Every
switchable session is now pre-sized to the attaching terminal, which moves that
repaint to attach time while the user is still looking at the first session,
and the switch binding restores `window-size latest` on arrival so a mid-attach
terminal resize still follows. Measured: 14 consecutive switches across 7
sessions, zero dot-padded rows, against 1-in-6 before.

⚠️ Known loose end, deliberately not papered over: after a detach the window
SIZE is restored exactly but the window-size MODE can come back as `latest`
rather than `manual`. The restore primitive round-trips correctly in isolation
(manual -> presize -> latest -> restore = manual) and no call site in the TUI
or the server sets `latest` afterwards, so the cause is not yet identified. The
practical effect is nil: the remaining client keeps the window at its own size
and Codeman re-pins `manual` on the browser's next resize.

src/tui/tui-client.ts

@@ -883,6 +883,43 @@ export class TuiClient {
     }
   }
 
+  /**
+   * Size a window to the terminal that is about to look at it, NOW.
+   *
+   * ⚠️ `window-size latest` only resizes a window while a client is actually on
+   * it. The sessions behind the tab strip have none until you switch, so the
+   * resize happened AT the switch: tmux painted the newly-available area with
+   * its dot fill, and an idle claude had no reason to redraw into it, leaving a
+   * pane in the corner of a dotted screen (reported from the beta, with a
+   * screenshot). Pre-sizing moves that repaint to attach time, while the user
+   * is still looking at the first session.
+   *
+   * `resize-window` with an explicit size implies `window-size manual`, which
+   * is what we want: the size is already right when the switch lands, so tmux
+   * has nothing to change and nothing to repaint. The switch binding puts
+   * `latest` back so a mid-attach terminal resize still follows.
+   */
+  async presizeWindow(muxName: string, cols: number, rows: number): Promise<boolean> {
+    if (!MUX_NAME_PATTERN.test(muxName)) return false;
+    if (!Number.isSafeInteger(cols) || !Number.isSafeInteger(rows) || cols <= 0 || rows <= 0) return false;
+    try {
+      await this.exec('tmux', [
+        '-L',
+        this.socket,
+        'resize-window',
+        '-t',
+        muxName,
+        '-x',
+        String(cols),
+        '-y',
+        String(rows),
+      ]);
+      return true;
+    } catch {
+      return false;
+    }
+  }
+
   /**
    * tmux's prefix key for a session (`C-b` unless the user's config says
    * otherwise), or null when tmux cannot say. Session-level first, then global:
@@ -963,7 +1000,27 @@ export class TuiClient {
   async bindSwitchKey(key: string, target: string): Promise<boolean> {
     if (!MUX_NAME_PATTERN.test(target)) return false;
     try {
-      await this.exec('tmux', ['-L', this.socket, 'bind-key', '-T', 'root', key, 'switch-client', '-t', target]);
+      // Two commands: go there, then let that window follow this terminal again.
+      // 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.
+      await this.exec('tmux', [
+        '-L',
+        this.socket,
+        'bind-key',
+        '-T',
+        'root',
+        key,
+        'switch-client',
+        '-t',
+        target,
+        ';',
+        'set-window-option',
+        '-t',
+        target,
+        'window-size',
+        'latest',
+      ]);
       return true;
     } catch {
       return false;