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/test/e2e-f1.test.ts

@@ -36,7 +36,7 @@ test("loop F1: crea sessione → SSE riceve il widget → risponde → il modell
       ollamaEnsure: async () => ({ ok: true }),
       searchPack: async () => {},
       sessionNew: async () => ({ id: "s1" }),
-      sessionShow: async (_id: string) => ({ id: "s1", provider: undefined, model: undefined, thinking: undefined }),
+      sessionShow: async (_id: string) => ({ id: "s1", interaction_language: "en", provider: undefined, model: undefined, thinking: undefined }),
       sessionList: async () => [],
     } as any,
     spawnFn: () => spawn("node", [FAKE, SCRIPT]) as any,
@@ -48,7 +48,7 @@ test("loop F1: crea sessione → SSE riceve il widget → risponde → il modell
   const created = await fetch(`${base}/sessions`, {
     method: "POST",
     headers: { "content-type": "application/json" },
-    body: JSON.stringify({ workspace: "w", question: "q" }),
+    body: JSON.stringify({ workspace: "w", question: "q", interactionLanguage: "en" }),
   });
   expect(created.status).toBe(200);