Restructure: Move final 12 root files into packages (klausur-service)

ocr/spell/  (3): smart_spell, core, text
upload/     (3): api, chunked, mobile
crawler/    (3): github, github_core, github_parsers
+ unified_grid → grid/, tesseract_extractor → ocr/engines/, htr_api → ocr/pipeline/

12 shims added. Only main.py, config.py, storage + RAG files remain at root.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

klausur-service/backend/upload/__init__.py

@@ -0,0 +1,6 @@
+"""
+Upload package — chunked and mobile upload endpoints.
+
+Moved from backend/ flat modules (upload_api*.py).
+Backward-compatible shim files remain at the old locations.
+"""