feat: add debug mode, distance-based thresholds, and improve pose detection

- Add debug mode support for encoding statistics in API responses
  - Debug info includes encoding length, min/max/mean/std, and first 10 values
  - Frontend logs encoding stats to browser console when debug enabled
  - Identify page enables debug mode by default

- Implement distance-based confidence thresholds for stricter matching
  - Borderline distances require higher confidence (70-95% vs 50%)
  - Applied when use_distance_based_thresholds=True (auto-match)
  - Reduces false positives for borderline matches

- Dual tolerance system for auto-match
  - Default tolerance 0.6 for regular browsing (more lenient)
  - Run auto-match button uses 0.5 tolerance with distance-based thresholds (stricter)
  - Auto-accept threshold updated to 85% (from 70%)

- Enhance pose detection with single-eye detection
  - Profile threshold reduced from 30° to 15° (stricter)
  - Detect single-eye visibility for extreme profile views
  - Infer profile direction from landmark visibility
  - Improved face width threshold (20px vs 10px)

- Clean up debug code
  - Remove test photo UUID checks from production code
  - Remove debug print statements
  - Replace print statements with proper logging

tests/README.md

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