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/pi-process-manager.test.ts

@@ -190,6 +190,29 @@ test("Pi receives the leased workspace runtime config and releases it on direct
   expect(release).toHaveBeenCalledOnce();
 });
 
+test("Pi language launch hint comes from the session options and never ambient environment", () => {
+  const previous = process.env.THT_INTERACTION_LANGUAGE;
+  process.env.THT_INTERACTION_LANGUAGE = "it";
+  const environments: NodeJS.ProcessEnv[] = [];
+  const mgr = new PiProcessManager(loadConfig({}), {
+    spawnFn: (_command, _args, options) => {
+      environments.push(options.env);
+      return recordingChild() as any;
+    },
+  });
+  try {
+    mgr.createFor("explicit-language", { interactionLanguage: "en" });
+    mgr.teardown("explicit-language");
+    mgr.createFor("manifest-resolved-in-gate");
+    mgr.teardown("manifest-resolved-in-gate");
+    expect(environments[0].THT_INTERACTION_LANGUAGE).toBe("en");
+    expect(environments[1]).not.toHaveProperty("THT_INTERACTION_LANGUAGE");
+  } finally {
+    if (previous === undefined) delete process.env.THT_INTERACTION_LANGUAGE;
+    else process.env.THT_INTERACTION_LANGUAGE = previous;
+  }
+});
+
 test("a close-only child event releases its temporary Pi agent snapshot", () => {
   const child = recordingChild();
   let snapshotDir: string | undefined;