refactor(ocr): make collapse_adjacent_markers a public function

Drop underscore prefix — the helper is part of confidence.py's effective
public API since spell_check.py imports and calls it directly.

Fixes reviewer concern: importing a _-prefixed name across module boundaries
contradicts Python's private-by-convention signal.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

ocr-service/confidence.py

@@ -9,7 +9,7 @@ ILLEGIBLE_MARKER = "[unleserlich]"
 CORRECTION_MARKER = "[?]"
 
 
-def _collapse_adjacent_markers(tokens: list[str]) -> list[str]:
+def collapse_adjacent_markers(tokens: list[str]) -> list[str]:
     collapsed: list[str] = []
     prev_was_marker = False
     for token in tokens:
@@ -52,7 +52,7 @@ def apply_confidence_markers(words: list[dict], threshold: float | None = None)
         else:
             tokens.append(word["text"])
 
-    return " ".join(_collapse_adjacent_markers(tokens))
+    return " ".join(collapse_adjacent_markers(tokens))
 
 
 def words_from_characters(prediction: str, confidences: list[float]) -> list[dict]:

ocr-service/spell_check.py

@@ -5,7 +5,7 @@ import os
 
 from spellchecker import SpellChecker
 
-from confidence import CORRECTION_MARKER, ILLEGIBLE_MARKER, _collapse_adjacent_markers
+from confidence import CORRECTION_MARKER, ILLEGIBLE_MARKER, collapse_adjacent_markers
 
 logger = logging.getLogger(__name__)
 
@@ -114,4 +114,4 @@ def correct_text(text: str) -> str:
         else:
             checked.append(ILLEGIBLE_MARKER)
 
-    return " ".join(_collapse_adjacent_markers(checked))
+    return " ".join(collapse_adjacent_markers(checked))