ui: Update parse level descriptions for hierarchy behavior

- Level 2: "content events with nested AsciiDoc"
- Level 3+: "index events" and "content events"
- Descriptions now match actual NKBIP-01 hierarchical behavior

✅ Verified: Level 3 with hierarchical content shows correct behavior
✅ Test: 2 chapters (==) → 30040 index events, 4 sections (===) → 30041 content events
✅ UI: 7 total events (1 root + 2 index + 4 content), preview shows hierarchy

Ready for: Preview panel hierarchy display enhancements

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/lib/components/ZettelEditor.svelte

@@ -109,10 +109,10 @@ import Asciidoctor from "asciidoctor";
       
       let label;
       if (level === 2) {
-        label = `Level ${level} (${equals} sections → events)`;
+        label = `Level ${level} (${equals} → content events with nested AsciiDoc)`;
       } else {
         const prevEquals = '='.repeat(level - 1);
-        label = `Level ${level} (${prevEquals} → indices, ${equals} → events)`;
+        label = `Level ${level} (${prevEquals} → index events, ${equals} → content events)`;
       }
       
       options.push({ level, label });