Add language-specific IPA and syllable modes (de/en)

Extend ipa_mode and syllable_mode toggles with language options:
- auto: smart detection (default)
- en: only English headword column
- de: only German definition columns
- all: all content columns
- none: skip entirely

Also improve English column auto-detection: use garbled IPA patterns
(apostrophes, colons) in addition to bracket patterns. This correctly
identifies English dictionary pages where OCR produces garbled ASCII
instead of bracket IPA.

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

klausur-service/backend/cv_syllable_detect.py

@@ -196,6 +196,7 @@ def insert_syllable_dividers(
     session_id: str,
     *,
     force: bool = False,
+    col_filter: Optional[set] = None,
 ) -> int:
     """Insert pipe syllable dividers into dictionary cells.
 
@@ -209,6 +210,8 @@ def insert_syllable_dividers(
     Args:
         force: If True, skip the pipe-ratio pre-check and syllabify all
             content words regardless of whether the original has pipe dividers.
+        col_filter: If set, only process cells whose col_type is in this set.
+            None means process all content columns.
 
     Returns the number of cells modified.
     """
@@ -247,6 +250,8 @@ def insert_syllable_dividers(
             ct = cell.get("col_type", "")
             if not ct.startswith("column_"):
                 continue
+            if col_filter is not None and ct not in col_filter:
+                continue
             text = cell.get("text", "")
             if not text:
                 continue