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.

backend/src/tht/interaction-language.ts

@@ -0,0 +1,10 @@
+/** Validate/canonicalize the tag; available translation catalogs belong to the UI. */
+export function interactionLanguage(value: unknown): string | undefined {
+  if (typeof value !== "string") return undefined;
+  try {
+    const [canonical] = Intl.getCanonicalLocales(value);
+    return canonical;
+  } catch {
+    return undefined;
+  }
+}

backend/src/tht/tht-runner.ts

@@ -59,6 +59,7 @@ export interface SessionRow {
   author: string | null;
   workspace_id?: string | null;
   workspace_revision?: string | null;
+  interaction_language?: string | null;
   archived?: boolean;
 }
 
@@ -482,6 +483,7 @@ export class ThtRunner {
 
   async sessionNew(o: {
     question: string;
+    interactionLanguage?: string;
     provider?: string;
     model?: string;
     thinking?: string;
@@ -497,6 +499,7 @@ export class ThtRunner {
       ["--provider", o.provider],
       ["--model", o.model],
       ["--thinking", o.thinking],
+      ["--interaction-language", o.interactionLanguage],
       ["--name", o.name],
       ["--workspace-id", o.workspaceId],
       ["--workspace-revision", o.workspaceRevision],
@@ -533,6 +536,12 @@ export class ThtRunner {
     return this.json<unknown>(["session", "show", id, "--json"], workspace);
   }
 
+  ensureInteractionLanguage(id: string, workspace?: string) {
+    return this.json<{ interaction_language: string }>(
+      ["session", "ensure-interaction-language", id, "--json"], workspace,
+    );
+  }
+
   sqlPreview(id: string, p: { limit?: number; offset?: number }, workspace?: string) {
     // No positional FILE: the harness resolves sql_final.sql from the session
     // via _session_sql_file(cfg, session_id), which respects the workspace path.