Add AI-powered selector suggestion

**Description:**
Suggest optimal selectors using AI analysis of page structure.

**Tasks:**
- [ ] Analyse DOM structure
- [ ] Generate selector candidates
- [ ] Rank by robustness
- [ ] Show suggestions in UI
- [ ] Test on various sites
- [ ] Add fallback logic
- [ ] Document algorithm

**Acceptance Criteria:**
- Suggestions relevant
- Robustness ranking is accurate
- UI helpful
- Fallback works