feat(cards): add 'note' card type for readable markdown content

New card type renders body as styled markdown with no copy/fill/run
affordance. Glyph: ¶, color: --note.

Migration uses transaction to safely rebuild table constraint.
Checks both 'note' presence and modified_at column to catch
partial migration state.

web/style.css

@@ -462,6 +462,7 @@ main.focus-peek .resize-handle { visibility: hidden; }
 .glyph-checklist { color: var(--remind); }
 .glyph-decision { color: var(--note); }
 .glyph-link { color: var(--event); }
+.glyph-note { color: var(--note); }
 
 .entity-content {
     flex: 1;