feat: show archived note indicator banner in editor #183

Shows a subtle ArchivedNoteBanner below the breadcrumb bar when a note is archived.

Changes

• ArchivedNoteBanner.tsx — muted banner with archive icon + Unarchive button (wired to same handler as Cmd+E)
• EditorContent.tsx — renders banner conditionally when entry.archived === true
• 3 new tests, all 1456 tests pass

Acceptance criteria

• Archived note shows subtle indicator below breadcrumb
• Editor remains fully editable (banner is purely informational)
• Indicator appears/disappears reactively via entry.archived from store
• Unarchive button calls same handler as Cmd+E

🎬 Cutter preview — PR #183

/note/some-archived-note-id — Archived banner appears above the note with a one-click Unarchive action.

Unarchive a note from banner — Unarchive action clears the archived banner and confirms the note is unarchived.