Add pasteToEditor(text) method that pastes text into the editor via
bracketed paste sequences, triggering paste handling (including collapse
for large content). Unlike setEditorText which directly replaces content,
pasteToEditor routes through handleInput on the active editor component.
- Add pasteToEditor to ExtensionUIContext interface
- Add handleInput to EditorComponent interface (was missing, all
concrete implementations already had it)
- Implement in interactive mode via bracketed paste sequence
- Add fallback in RPC mode (delegates to setEditorText)
- Document in extensions.md
setCustomEditorComponent() was not copying the paddingX setting from
the default editor to extension-provided editors. Also propagate live
changes from the settings callback.