Attach panels to a sketch (notes linking)

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User Story: As an analyst building an investment thesis, I want to attach analyst result panels, news article links, and free text from anywhere in the app to the notes panel of a specific idea/sketch, so that all the evidence supporting one thought experiment lives in one place.
Acceptance Criteria:

• On any AI analyst result panel (Technical, Fundamentals, News, Sentiment, Research Verdict), an "attach to idea" affordance — keyboard-first, e.g. A while focused on the panel — opens an autocomplete picker of saved sketches.
• On any news card / article reader / SEC filing row, the same A keybinding works.
• Selecting a sketch appends a structured reference to that sketch's notes panel: [2026-05-10] {kind}: {title} — {url-or-snippet}.
• References in the notes panel become clickable — clicking opens the original (article reader, AI panel, etc.) without leaving /ideas.
• Free text typed directly in the notes textarea continues to be persisted as-is (existing behavior).

Technical Notes:

• The notes column is plain TEXT today. Could stay as Markdown-ish text with a renderer pass, or move to a structured sketch_attachments table for clickability. Markdown-with-links is faster to ship; structured table is cleaner long-term.
• The _ideasGetSketches() window helper from PR feat: ideas sketchpad — comparative graphs across metrics (idea #2) #48 already exposes the sketch list — reuse for the picker dropdown.
• Reuse the article-reader slide-in panel for opening attached articles, same as elsewhere.