refactor: migrate translate engine to GRACE-Poly v2.6 semantic protocol

- Convert all 84 contracts from legacy [DEF:] to #region/#endregion syntax
- Fix complexity tiers: 14 modules re-tiered (6 C4 route modules, 7 C4→C5 plugin services)
- Remove forbidden tags: @RATIONALE/@REJECTED stripped from C1–C4 contracts
- Add required tags: @PRE/@POST/@SIDE_EFFECT on C4, @RELATION on C3, @DATA_CONTRACT/@INVARIANT on C5
- Add belief runtime markers (reason/reflect/explore) to 7 service.py functions
- Fix @LAYER: route files → UI, plugins → Domain, superset_executor → Infra
- Fix pre-existing test mock_service fixture in test_orchestrator.py
- 196/196 translation tests pass, zero regressions

backend/src/plugins/translate/_utils.py

@@ -1,30 +1,22 @@
-# [DEF:DictionaryUtils:Module]
-# @COMPLEXITY: 1
-# @SEMANTICS: dictionary, utils, normalize, delimiter
-# @PURPOSE: Utility helpers for dictionary management (term normalization and delimiter detection).
-# @LAYER: Domain
+# #region DictionaryUtils [C:1] [TYPE Module]
+# #endregion DictionaryUtils
 
 import re
 import unicodedata
 
 
-# [DEF:_normalize_term:Function]
-# @PURPOSE: Normalize a term for case-insensitive unique constraint lookup.
-# @RATIONALE: NFC normalization is applied before lowercasing to ensure consistent
-#             comparison of Unicode characters (e.g. precomposed vs decomposed forms).
-# @REJECTED: Lowercasing without NFC normalization — would cause duplicate entries
-#            for semantically identical Unicode strings in different normalization forms.
+# #region _normalize_term [C:2] [TYPE Function] [SEMANTICS dictionary,normalize]
+# @BRIEF Normalize a term for case-insensitive unique constraint lookup using NFC normalization.
 def _normalize_term(term: str) -> str:
     """Normalize a term by NFC, lowercasing, and removing extra whitespace."""
     if not term:
         return ""
     term = unicodedata.normalize('NFC', term)
     return " ".join(term.lower().split())
-# [/DEF:_normalize_term:Function]
+# #endregion _normalize_term
 
 
-# [DEF:_detect_delimiter:Function]
-# @PURPOSE: Detect the delimiter used in a CSV/TSV header line.
+# #region _detect_delimiter [C:1] [TYPE Function] [SEMANTICS dictionary,delimiter]
 def _detect_delimiter(header_line: str) -> str:
     """Detect delimiter by counting tabs vs commas in the first line."""
     if not header_line:
@@ -32,4 +24,4 @@ def _detect_delimiter(header_line: str) -> str:
     tab_count = header_line.count("\t")
     comma_count = header_line.count(",")
     return "\t" if tab_count > comma_count else ","
-# [/DEF:_detect_delimiter:Function]
+# #endregion _detect_delimiter