Add adaptive preprocessing escalation and single-receipt test scripts

Preprocessing now tries progressively heavier variants per receipt
(plain -> high-pass -> edge-enhance -> both), stopping as soon as a
cheap LLM-free arithmetic check on the OCR text looks plausible, so
the extra processing only applies to receipts that need it. A flat
version of the same heavier processing regressed the full batch by
helping hard receipts but hurting easy ones; the adaptive version
improves date-matching 37/52 -> 40/52 with no regression (see
testing/2026_10_04_gimp_highpass_nlfilter_experiment.md).

Also adds test_ocr.sh and test_single.sh for checking a single
receipt's OCR text or full pipeline result without a batch run.

test_batch.sh

@@ -1,17 +1,20 @@
 #!/usr/bin/env bash
-# Test-only tool: runs the full container pipeline (1_preprocess_image.sh,
-# 2_ocr_image.sh, 3_extract_data.sh) over every *.jpg in a test-data
-# directory, then compares the results against that directory's
-# ground-truth spreadsheet (benzin_kosten.ods). Everything -
+# Test-only tool: runs the full container pipeline
+# (12_adaptive_preprocess_ocr.sh, 3_extract_data.sh) over every *.jpg in
+# a test-data directory, then compares the results against that
+# directory's ground-truth spreadsheet (benzin_kosten.ods). Everything -
 # preprocessing, OCR, structuring, and the comparison itself - runs
 # inside the tooling container; nothing here depends on a host Python
 # environment.
 #
 # For an input directory <path>/<name>, two sibling directories are
 # created (mirroring <path>/<name>):
-#   <path>/<name>-scratch/<receipt>/  - intermediate step output
-#                                       (01_gray.png, 02_bilateral.png,
-#                                       03_final.png, ocr.txt) for
+#   <path>/<name>-scratch/<receipt>/  - intermediate step output: one
+#                                       variant<N>/ subdir per
+#                                       preprocessing variant tried
+#                                       (01_gray.png, ..., 0X_final.png,
+#                                       ocr.txt each) plus ocr.txt for
+#                                       the winning variant, for
 #                                       inspecting each step on its own
 #   <path>/<name>-result/<receipt>/   - final extracted.json per receipt,
 #                                       plus summary.txt with the overall
@@ -56,8 +59,7 @@ for img in "${IMAGES[@]}"; do
     receipt_result="$RESULT_DIR/$name"
     mkdir -p "$receipt_scratch" "$receipt_result"
     echo "--- $name ---"
-    ./1_preprocess_image.sh -in "$img" -out "$receipt_scratch" >/dev/null
-    ./2_ocr_image.sh -in "$receipt_scratch/03_final.png" -out "$receipt_scratch" >/dev/null
+    ./12_adaptive_preprocess_ocr.sh -in "$img" -out "$receipt_scratch" >/dev/null
     ./3_extract_data.sh -in "$receipt_scratch/ocr.txt" -out "$receipt_result" >/dev/null
 done