Add full shell, replaceable Omics adapter and bilingual interaction

Implement approved specification #32 and tickets #33-#37. Keep host authentication server-verified and pin session interaction language. Compile scoped base selectors for browser compatibility and retain full gutters during CSS pruning.

harness/tht/session/models.py

@@ -8,7 +8,7 @@ from typing import Literal, Self
 
 import portalocker
 import yaml
-from pydantic import BaseModel, ConfigDict, Field
+from pydantic import BaseModel, ConfigDict, Field, field_validator
 
 from tht.decisions import DecisionRecord
 
@@ -119,10 +119,18 @@ class SessionManifest(_YamlModel):
     thinking: str | None = None
     workspace_id: str | None = None
     workspace_revision: str | None = None
+    interaction_language: str | None = None
     name: str | None = None
     archived: bool = False
     group: str | None = None
 
+    @field_validator("interaction_language")
+    @classmethod
+    def valid_interaction_language(cls, value: str | None) -> str | None:
+        from tht.session.language import validate_language_tag
+
+        return validate_language_tag(value) if value is not None else None
+
 
 class SessionSnapshot(BaseModel):
     """The current persisted session state, excluding the non-persistent chat stream."""