- Enforce explicit-any and TypeScript suppression bans in tests
- Remove remaining broad any casts from engine and e2e coverage
- Split markdown ambient declarations from typed browser globals
styleRuns were updated on the graph during editing (via syncText) but
commitTextEdit only captured text changes. Now both text and styleRuns
are snapshotted at startTextEditing and restored on undo.
commitTextEdit compared prevText from the scene graph node, but
syncText already updates the node on every keystroke during editing.
This made prevText === newText, so the undo entry was never pushed.
Fix: capture the original text when startTextEditing is called and
use that snapshot for the undo comparison.
