ISSUE-015 — Concept explanation content adapter

[shivaram19]

• Functional surgeon view: Concept explanations are scraped/adapted once and cached, not regenerated per request.
• Acceptance criteria:
  1. New ConceptAdapter port + adapter.
  2. Adapted content stored in DB or JSON.
  3. Weak-area links read from cache.
• Dependencies: ISSUE-002 (weak-area links).