feat(graph): notes render as parentless stars in the stellar field

[diogobaltazar]

Description

Notes captured in Move37 have no task parent — they are free-standing thoughts rather than work items. Visually they should reflect this: notes appear in the stellar field as stars (same appearance as completed-node stars from #38) but with no sphere position and no parent edge. They float freely in the outer field, unanchored, like solitary stars between constellations.

Relationship to #38

This issue depends on the stellar field and star appearance introduced in #38, but is independent in scope — it concerns a different node type (notes vs. completed tasks) and a different placement rule (no depth-ring, truly parentless).

Visual behaviour

• Position: Notes are placed in the stellar field without belonging to any depth-ring level. Their positions are distributed across the outer space independently of the sphere geometry.
• Appearance: Same star glow as completed nodes (feat(graph): completed nodes orbit as stars around the task sphere #38) — bright core, soft radial bloom, accent palette.
• Edges: None. Notes have no parent, so no edges are drawn to or from them in the default view.
• Interaction: Notes remain clickable/double-clickable to open the note editor, consistent with existing behaviour.

Acceptance criteria

• Notes are rendered in the stellar field as star-shaped nodes with the glow style from feat(graph): completed nodes orbit as stars around the task sphere #38.
• Notes have no edges to any other node.
• Note positions are stable across re-renders (deterministic placement).
• Creating a new note causes it to appear in the stellar field without disturbing the sphere layout.
• Deleting a note removes it from the stellar field.
• No regression to task-node or completed-node rendering.