Closes the architectural piece of the "MCP element toolset" P1 gap
(TS pen-mcp ships ~100 add_card_*/add_toast_* element tools).
- op-editor-core: new `EditorCommand::InstantiateKitComponent`
variant + applier branch that calls
`EditorState::instantiate_kit_component` with the requested
drop point (defaults to (0, 0)).
- op-mcp: `element_tools.rs` — `InsertKitComponent` per-component
tool returning `OkWithCommand(_, InstantiateKitComponent)`;
`insert_kit_component_tools(state)` walks every loaded kit;
`element_tool_schemas(state)` emits the matching tools/list
JSON. Tool names sanitize dashes: `insert_btn_primary`,
`insert_card_basic`, etc.
- op-host-desktop: `rebuild_registry` chains the dynamic tools
in; `tools_list_response` takes EditorState and appends the
dynamic schemas next to TOOL_SCHEMAS.
- op-editor-core: tidies the empty-pages `ensure_pages` guard to
`is_none_or`.
Result: 6 starter-kit components → 6 working MCP tools. The 100-tool
catalog parity is now a data fill-in (more components in op-editor-
core/uikit.rs auto-register as more MCP tools).
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