Detect and confirm page orientation during automatic splitting

Bundle the trained heatmap/image orientation model and run it after provisional
blank-page and split analysis. Confirm candidates with Gemini using low thinking;
resolve mixed A3 sheet ordering with the complete statement and medium thinking.
Keep A4 scans independent and export paired A3 scans in booklet reading order.

Reanalyse uniformly inverted source sheets, validate ordering permutations, and
preserve source provenance, corrected rotations and reading slots in manual review.
Document the experiments, rejected approaches, calibration and runtime limits.

Validation: focused splitting/orientation regression suites pass; bundled model
checksum and wheel assets verified. Full Interro07 offline run: 44.26 seconds,
eight candidates, mocked upright confirmations, source hashes and geometry intact.

default_config.py

@@ -2,6 +2,8 @@ import os
 from pathlib import Path
 
 API_KEY = os.environ.get("GEMINI_API_KEY")
+# None inherits MODEL_FOR_LABEL_ID, including existing personal overrides.
+MODEL_FOR_PAGE_ORIENTATION = None
 
 EXPORT_DIR = Path("Export")
 IMPORT_DIR = Path("Import")