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.

README.md

@@ -45,6 +45,10 @@ tooling-container/     Pipeline source (preprocess.py, ocr.py, extract.py,
 test_batch.sh           Runs the full pipeline over a directory of test
                         receipts and compares against its ground-truth
                         .ods - see AGENT.md's "Current state".
+test_single.sh          test_batch.sh for one receipt instead of a
+                        directory - re-check a single known failure.
+test_ocr.sh             Preprocessing + OCR only, prints the raw OCR
+                        text to stdout - no files left behind.
 docker-compose.yml      Runs the pipeline as a long-lived HTTP job API
                         (api + ollama services) for the Android app.
 android/                The Android app: Kotlin + Jetpack Compose, Room
@@ -134,6 +138,19 @@ receipt at a time:
                                            # file in that directory
 ```
 
+**Re-check one receipt** (ground truth optional - compared if a `*.ods`
+is found next to the photo):
+
+```bash
+./test_single.sh -in testdata/<some-set>/some-receipt.jpg
+```
+
+**Just see what Tesseract reads**, no LLM call, no files left behind:
+
+```bash
+./test_ocr.sh -in testdata/<some-set>/some-receipt.jpg
+```
+
 **Serve it for the app**:
 
 ```bash