feat(dashboard): integrate link suggestions and predictive links into UI

- FastAPI: parse_engram now includes link_suggestions and predictive_links from metadata
- FastAPI: add POST /api/links/accept to create links from suggestions
- Dashboard: new renderCardsWithSuggestions() displays suggestions in each card
- Dashboard: acceptLink() function handles click-to-link
- Dashboard: loadCards() calls renderCardsWithSuggestions()
- Systemd: remove DirectoryNotEmpty from ingest path unit (already present)

Refs: #25 #27

systemd/openclaw-secondbrain-ingest-memory.path

@@ -4,7 +4,6 @@ PartOf=openclaw-secondbrain.target
 
 [Path]
 PathModified=/root/.openclaw/workspace/memory
-DirectoryNotEmpty=true
 
 [Install]
 WantedBy=multi-user.target