feat: expose and delete FigJam pen/ink (VectorPath) nodes via apply_patch

[hugolytics]

Observed

Handwritten ink/pencil drawings made with FigJam's pen tool are invisible to the bridge. They do not appear in canvas_read D2 output or id_map, and cannot be targeted by apply_patch delete ops.

Repro

1. Draw something with FigJam's pen tool on a canvas the bridge is connected to.
2. Call canvas_read — the ink strokes are absent from d2_view.diagram.d2 and id_map.
3. Attempt to delete via apply_patch — no node ID available to target.

Expected

Ink/vector nodes should be surfaced in canvas_read (even as opaque entries with a type tag like type: ink) so they can be targeted for deletion via apply_patch { type: 'delete', node_id: '...' }.

Full round-trip read/write support for ink is not required — delete is the primary use case.

Root cause

The plugin's canvas serialization only handles SHAPE_WITH_TEXT, SECTION, and CONNECTOR node types. FigJam pen strokes are likely VectorNode or a similar type and are skipped during serialization.

Proposed implementation

1. In the plugin's canvas read pass, collect nodes of type VECTOR / pen stroke and include them in the snapshot with type: 'ink' and their figmaId.
2. In apply_patch, the existing delete handler already calls figma.getNodeById — no change needed there, as long as the ID is surfaced.
3. canvas_write_d2 does not need to handle ink nodes — they can be omitted from D2 diffing (read-only in D2 view, delete-only via apply_patch).

Workaround today

User must manually select and delete ink strokes in FigJam.