feat(tui): add zoom to the session view actions menu

[edwin-zvs]

The pane actions menu (☰ on a session view's title bar) covered split / close split but not zoom, so the fullscreen toggle was keyboard-only (C-x z / z). This adds a zoom row between the splits and close split, labelled with the active profile's chord like every other row.

 ● s1           ────────────────────────────── shell ─ ☰  ┐
│                        ┌ session ───────────────────────┐
│                        │rename                     C-x r│
│                        │fork                       C-x f│
│                        │playbook mode          C-x Space│
│                        │split horizontal           C-x 3│
│                        │split vertical             C-x 2│
│                        │zoom                       C-x z│
                         │close split                C-x 0│
                         │archive                    C-x k│
                         │merge and archive               │
                         │delete                     C-x k│
                         │copy id (s1)                    │
                         └────────────────────────────────┘

Why it isn't just run_action(ToggleZoom): the chord derives its target from the focused pane (List → zoom the list, View → zoom the view). A menu click can land while focus is still the session list, so the row pins the target to the view the menu hangs off, then toggles.

Getting back out stays keyboard/palette (C-x z, z, /zoom) — the zoomed layout is deliberately borderless, so there's no title bar to reopen the menu from. That's unchanged by this PR; mentioning it because the row reads zoom, not a toggle label.

Not included: the operator (minibuffer) pane's title menu, which shows the same split / close-split pane actions. Easy follow-up if you want the pair to match.

Testing

• New unit test session_menu_zoom_row_zooms_the_view_pane: opens the menu by clicking ☰ with focus on the list, clicks the row, asserts ZoomMode::View + focus follows + menu closes.
• cargo test --workspace green (daemon_drop_reaps_shell_adapter_tree flaked once under concurrent build load, passes on rerun).

Relevant binary: construct (this PR only touches crates/cli) — .claude/worktrees/tui-session-menu-zoom/target/debug/construct