fix(tui): let Tab indent a multi-line Playbook selection; C-o focuses the menu

[edwin-zvs]

Closes #1106.

Spec 0094 gives Tab / S-Tab list nesting that operates on every list line the selection spans — but the selection action menu claimed bare Tab first, to focus itself, so the multi-line half was unreachable. S-Tab wasn't claimed, leaving the pair asymmetric: a selected block could be un-nested but never nested.

What changed

crates/cli/src/app/editor.rs — the unfocused menu now claims C-o instead of Tab. While the menu is merely shown, every editing key — including Tab/S-Tab indent over the selection — keeps reaching the editor. Once focused, menu behavior is unchanged (Up/Down/Tab/BackTab cycle rows, Esc unfocuses, Enter runs).

Why C-o: reliable in every terminal (unlike M-Enter, which dies on macOS terminals not configured to send Option as Meta), free in the playbook keymap, and consistent with the editor's emacs-flavored chord family. Only C-x chords are claimed globally, so there's no collision.

crates/cli/src/ui.rs — the passive menu advertises the chord: a dim C-o menu bottom-border title, shown only while unfocused. This also closes the discoverability half of #1092 (nothing on the menu ever said how to reach it); #1092's remaining half (what Enter should do while the menu is passive) is deliberately left to that issue.

specs/0196-playbook-selection-menu-focus-model.md — records the rule: a passive popup may not steal keys the surface underneath documents, and the focus chord must be advertised on the menu frame.

Acceptance criteria from the issue

• ✅ Tab with a multi-line selection indents every list line the selection spans (repro test: - one\n- two\n- three with lines 1–2 selected → both nest)
• ✅ S-Tab keeps outdenting the same lines (asserted on the remapped selection right after the indent)
• ✅ The menu is still keyboard-reachable, by an advertised key (C-o, rendered on the menu; render test asserts the hint)

Testing

• Replaced the old playbook_tab_focuses_selection_menu_for_multi_line_selection test (which enshrined the bug) with the issue's repro + a C-o-focuses test.
• Updated the four menu tests that used Tab as the focus vehicle (comment editing, emacs keys, verb navigation, render highlight) to C-o.
• cargo test -p construct-cli --bin construct playbook: 333 passed. Full workspace suite running before merge.

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