Adds user-facing control over the editor tab width.
New methods on Editor (editor/mod.rs):
tab_width() -> usize
- Returns current visual tab width in spaces.
set_tab_width(width: usize)
- Sets tab width, clamped to min 1.
cycle_tab_width() -> usize
- Cycles 4 → 8 → 2 → 4 (default 4 → wider → narrower → back).
- Returns the new width.
Alt-T binding (editor/handlers.rs):
try_global_shortcut now handles Alt-T (0x74) and calls
cycle_tab_width(). Status bar shows 'Tab width: N'.
Tab-to-indent (B3) and word-wrap (B1) both consume tab_width
via the field, so changing it via Alt-T takes effect immediately
on next render / insert.
Tests (5 new in editor::tests):
- tab_width_default_is_four
- set_tab_width_updates_field (verifies 0 → 1 clamp)
- cycle_tab_width_advances_2_4_8_2
- cycle_tab_width_from_unusual_value_resets_to_2
- tab_to_indent_uses_current_tab_width
Config wiring note: cfg.editor.tab_width (config.rs) already has
the field with serde defaults and persistence. Wiring it into
Editor::open() requires the constructor to accept &Config and
is deferred to a future sprint.
Total: 1253 passing (was 1248; +5 new).
kellito
d4ddc4e2c7