feat(viz): Add dual-score display and improve UI controls

This commit enhances the vector visualization interface with better score
transparency and improved UX:

**Dual-Score Display:**
- Store original algorithm scores before normalization (viz_routes.py:203)
- Display both raw and normalized scores: "Raw Score: 0.842 (89% relative)"
- Update plot hover text with dual scores (userinfo_routes.py:740)
- Fixes issue where all queries showed at least one 100% match regardless
  of actual relevance (normalization artifact)

**UI Improvements:**
1. Fusion Method dropdown: Changed from x-show to :disabled
   - Prevents jarring layout shift when switching algorithms
   - Dropdown stays visible but grayed out when Semantic is selected
   - Better UX with opacity: 0.5 and cursor: not-allowed

2. Score Threshold: Changed step from 0.1 to "any"
   - Allows arbitrary float precision (0.7, 0.85, 0.123)
   - Users can now fine-tune threshold values

3. Document Types: Converted multi-select to checkbox grid
   - Replaced clunky Ctrl/Cmd multi-select listbox
   - Checkbox grid with cleaner layout
   - Positioned left of Score Threshold and Result Limit inputs
   - More intuitive UX

**Technical Details:**
- Raw score ranges vary by algorithm:
  - Semantic: 0.0-1.0 (cosine similarity)
  - BM25 RRF: ~0.001-0.033 (Reciprocal Rank Fusion)
  - BM25 DBSF: Can exceed 1.0 (Distribution-Based Score Fusion)
- Normalized scores (0-1) used for visual encoding (marker size, color)
- Original scores preserved in API response via getattr fallback

Files modified:
- nextcloud_mcp_server/auth/viz_routes.py (store original_score)
- nextcloud_mcp_server/auth/templates/vector_viz.html (UI controls)
- nextcloud_mcp_server/auth/userinfo_routes.py (plot hover text)

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

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

nextcloud_mcp_server/auth/userinfo_routes.py

@@ -737,7 +737,7 @@ async def user_info_html(request: Request) -> HTMLResponse:
                             y: coordinates.map(c => c[1]),
                             mode: 'markers',
                             type: 'scatter',
-                            text: results.map(r => `${{r.title}}<br>Score: ${{r.score.toFixed(3)}}`),
+                            text: results.map(r => `${{r.title}}<br>Raw Score: ${{r.original_score.toFixed(3)}} (${{(r.score * 100).toFixed(0)}}% relative)`),
                             marker: {{
                                 // Multi-channel encoding: size + opacity + color for visual hierarchy
                                 // Power scaling (score^2) amplifies visual differences dramatically