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/plugin.py

@@ -1,19 +1,15 @@
-# [DEF:TranslatePlugin:Module]
-# @COMPLEXITY: 2
-# @SEMANTICS: plugin, translate, llm, sql, dashboard
-# @PURPOSE: TranslatePlugin skeleton for cross-dialect SQL and dashboard translation.
-# @LAYER: Domain
-# @RELATION: INHERITS -> [PluginBase]
-# @RATIONALE: Separate plugin avoids bloating LLMAnalysisPlugin beyond fractal limit (<400 lines).
-# @REJECTED: Extending LLMAnalysisPlugin would conflate two distinct feature domains.
+# #region TranslatePlugin [C:3] [TYPE Module] [SEMANTICS plugin,translate,llm,sql,dashboard]
+# @BRIEF TranslatePlugin skeleton for cross-dialect SQL and dashboard translation.
+# @LAYER Domain
+# @RELATION INHERITS -> [PluginBase]
 
 from typing import Dict, Any, Optional
 from ...core.plugin_base import PluginBase
 
 
-# [DEF:TranslatePlugin:Class]
-# @PURPOSE: Plugin for translating SQL queries and dashboard definitions across database dialects.
-# @RELATION: IMPLEMENTS -> backend.src.core.plugin_base.PluginBase
+# #region TranslatePlugin [C:3] [TYPE Class] [SEMANTICS plugin,translate]
+# @BRIEF Plugin for translating SQL queries and dashboard definitions across database dialects.
+# @RELATION IMPLEMENTS -> [PluginBase]
 class TranslatePlugin(PluginBase):
     @property
     def id(self) -> str:
@@ -57,6 +53,6 @@ class TranslatePlugin(PluginBase):
     async def execute(self, params: Dict[str, Any], context: Optional[Any] = None):
         """Execute a translation job — implementation deferred to later phases."""
         raise NotImplementedError("TranslatePlugin.execute not yet implemented")
-# [/DEF:TranslatePlugin:Class]
+# #endregion TranslatePlugin
 
-# [/DEF:TranslatePlugin:Module]
+# #endregion TranslatePlugin