feat(observer): v15 AG Native chat relay — scanChatBodies dual strategy (#632)

- Add AG Native DOM path: #conversation + .leading-relaxed.select-text
- Keep Cascade path: [data-testid=conversation-view] + [data-step-index]
- Register #632 in known-issues.md (SDK+DOM both blocked for AG Native)
- Bump version 0.5.50 → 0.5.51
- Add DOM analysis helper scripts

.agents/workflows/helpers/parse_dump.py

@@ -0,0 +1,19 @@
+import json, os, sys
+
+dump_path = os.path.join(os.path.expanduser('~'), '.gemini', 'antigravity', 'bridge', 'dump_html.json')
+with open(dump_path, 'r', encoding='utf-8') as f:
+    data = json.load(f)
+
+qi = data.get('quickInfo', {})
+print('=== Quick Info ===')
+print('hasConversationView:', qi.get('hasConversationView'))
+print('hasStepIndex:', qi.get('hasStepIndex'))
+print('hasBotColor:', qi.get('hasBotColor'))
+print('hasMarkdownBody:', qi.get('hasMarkdownBody'))
+print('hasProse:', qi.get('hasProse'))
+print('totalElements:', qi.get('totalElements'))
+print('dataTestIds:', qi.get('dataTestIds'))
+print('dataAttrs (first 20):', qi.get('dataAttrs', [])[:20])
+print('buttons (first 10):')
+for b in qi.get('buttons', [])[:10]:
+    print(f"  [{b.get('tag')}] {b.get('text', '')[:60]}  visible={b.get('visible')}")