feat: refine notes workspace and add canvas zoom

Simplify sidebar selection and note record framing, compact the empty composer, and emphasize note titles. Replace redundant AI comment headings with an accessible panel toggle.

Add view-only canvas zoom and fit width, correct PDF import/export icons, and allow image files up to 20 MiB. Include regression coverage and updated design documentation.

Release note: Notes have clearer navigation and a more compact writing area. Canvases support zoom and fit width, and image imports accept files up to 20 MiB.

src/main/magic-notes/canvas-ipc.integration.test.ts

@@ -219,6 +219,22 @@ describe('production preload -> registered IPC -> SQLite canvas persistence', ()
     expect(await api.get(note.id)).toEqual(saved)
   })
 
+  it('saves and reopens a 20 MiB canvas image through create and update IPC', async () => {
+    const content = canvas()
+    const bytes = Buffer.alloc(20 * 1024 * 1024)
+    Buffer.from(png.split(',')[1]!, 'base64').copy(bytes)
+    content.assets[0]!.dataUrl = `data:image/png;base64,${bytes.toString('base64')}`
+    const note = await api.create({ title: 'Large canvas image' })
+    const created = await api.createEntry({ noteId: note.id, content })
+    await reopen()
+    const entry = (await api.get(note.id)).entries.find(item => item.id === created.createdEntryId)!
+    expect(entry.content).toEqual(content)
+    content.flow!.ops[0] = { insert: 'Edited large image note' }
+    await api.updateEntry({ entryId: entry.id, expectedRevision: entry.revision, content })
+    await reopen()
+    expect((await api.get(note.id)).entries.find(item => item.id === entry.id)!.content).toEqual(content)
+  })
+
   it('preserves a real generated PDF and all page references through three reopen/save cycles', async () => {
     const { jsPDF } = await import('jspdf')
     const pdf = new jsPDF()