UI: Korean, Japanese and Chinese input and interface text (#101)

The slide turns the input method on while it takes typing, with the candidate window at the
caret, and forwards egui Ime events to text.compose / text.commit, so a Korean keyboard composes
syllables instead of separate jamo. Interface text in scripts the interface fonts lack (Hangul,
Simplified Chinese, Thai...) borrows faces from the font database (installed fonts such as Malgun
Gothic; nothing bundled): file names, titles, notes, outline, sections, comments and typed text.
Ported and widened from WordCraft's #565/#840 fallback. The notes pane keeps text typed before
focus leaves in the same frame (Escape, another slide). Control channel: ui.ime.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/control-protocol.md

@@ -19,6 +19,7 @@ Coordinates are slide points (1/72 inch; a 16:9 slide is 960 × 540) unless note
 | `ui.tool.select` | `{tool, preset?}` | `select`, `text`, `shape` + preset, any preset name, `curve`, `freeform`, `scribble`, `pen`, `highlighter`, `eraser` |
 | `ui.pointer` | `{events: [{kind: down\|drag\|up\|move\|doubleclick\|tripleclick, x, y, mods?}], mods?}` | Drive the active tool in slide points through the same code path as the mouse |
 | `ui.key` / `ui.text` | `{key, shift?, alt?, cmd?}` / `{text}` | Keyboard input (also drives a running slide show) |
+| `ui.ime` | `{preedit, active?: [start, end]}` / `{commit}` | An input method's composition through egui, as a real one arrives: shown in place on the slide or in a focused field; `{"preedit": ""}` cancels |
 | `ui.move` / `ui.click` / `ui.drag` | screen points | Real egui pointer input — reaches every widget, menu and pane |
 | `ui.set` | `{tab?, view?, pane?, notes?, zoom?, brightness?, ruler?, gridlines?, guides?, …}` | UI state (returns the full state) |
 | `ui.dialog.open` / `ui.dialog.close` | `{id, fields?}` | Open or close a dialog by id; `fields` pre-fills its fields (About: `{"tab": "contributors"}` or `"models"`) |