Add margin check to multi-ref matching to reduce false positives

The multi-ref matching method was missing a margin check against other
logos, causing excessive false positives. This fix adds:

- margin parameter to find_best_match_multi_ref() that requires the
  best logo's score to exceed the second-best by a minimum margin
- Test script now passes --margin to both matching methods
- Updated documentation to reflect margin applies to both methods

Also adds run_comparison_tests.sh to run all three matching methods
and compare results.

run_comparison_tests.sh

@@ -0,0 +1,76 @@
+#!/bin/bash
+#
+# Run logo detection tests with all three matching methods and save results.
+#
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+OUTPUT_FILE="${SCRIPT_DIR}/comparison_results.txt"
+
+# Common parameters
+NUM_LOGOS=20
+REFS_PER_LOGO=10
+POSITIVE_SAMPLES=20
+NEGATIVE_SAMPLES=100
+MIN_MATCHING_REFS=3
+
+# Use a fixed seed for reproducibility across methods
+SEED=42
+
+echo "Logo Detection Comparison Tests" > "$OUTPUT_FILE"
+echo "================================" >> "$OUTPUT_FILE"
+echo "Date: $(date)" >> "$OUTPUT_FILE"
+echo "" >> "$OUTPUT_FILE"
+
+echo "Running tests with:"
+echo "  Reference logos: $NUM_LOGOS"
+echo "  Refs per logo: $REFS_PER_LOGO"
+echo "  Positive samples: $POSITIVE_SAMPLES"
+echo "  Negative samples: $NEGATIVE_SAMPLES"
+echo "  Min matching refs: $MIN_MATCHING_REFS"
+echo "  Seed: $SEED"
+echo ""
+
+# Test 1: Margin-based matching
+echo "=== Test 1: Margin-based matching ===" | tee -a "$OUTPUT_FILE"
+uv run python "$SCRIPT_DIR/test_logo_detection.py" \
+    --num-logos $NUM_LOGOS \
+    --refs-per-logo $REFS_PER_LOGO \
+    --positive-samples $POSITIVE_SAMPLES \
+    --negative-samples $NEGATIVE_SAMPLES \
+    --matching-method margin \
+    --seed $SEED \
+    2>&1 | tee -a "$OUTPUT_FILE"
+
+echo "" >> "$OUTPUT_FILE"
+echo "" >> "$OUTPUT_FILE"
+
+# Test 2: Multi-ref with mean similarity
+echo "=== Test 2: Multi-ref matching (mean similarity) ===" | tee -a "$OUTPUT_FILE"
+uv run python "$SCRIPT_DIR/test_logo_detection.py" \
+    --num-logos $NUM_LOGOS \
+    --refs-per-logo $REFS_PER_LOGO \
+    --positive-samples $POSITIVE_SAMPLES \
+    --negative-samples $NEGATIVE_SAMPLES \
+    --matching-method multi-ref \
+    --min-matching-refs $MIN_MATCHING_REFS \
+    --seed $SEED \
+    2>&1 | tee -a "$OUTPUT_FILE"
+
+echo "" >> "$OUTPUT_FILE"
+echo "" >> "$OUTPUT_FILE"
+
+# Test 3: Multi-ref with max similarity
+echo "=== Test 3: Multi-ref matching (max similarity) ===" | tee -a "$OUTPUT_FILE"
+uv run python "$SCRIPT_DIR/test_logo_detection.py" \
+    --num-logos $NUM_LOGOS \
+    --refs-per-logo $REFS_PER_LOGO \
+    --positive-samples $POSITIVE_SAMPLES \
+    --negative-samples $NEGATIVE_SAMPLES \
+    --matching-method multi-ref \
+    --min-matching-refs $MIN_MATCHING_REFS \
+    --use-max-similarity \
+    --seed $SEED \
+    2>&1 | tee -a "$OUTPUT_FILE"
+
+echo ""
+echo "Results saved to: $OUTPUT_FILE"