refactor(open-sse): remove reverse coupling open-sse -> src (E2)

Move clineAuth into open-sse/shared (src re-exports back). Add standalone
open-sse/shared/machineId for codex session hashing (no @/lib/dataDir).
sttCore receives sttConfig via param instead of importing AI_PROVIDERS.
No behavior change; gate: no regression (26 known-fails unchanged).

Co-authored-by: Cursor <cursoragent@cursor.com>

open-sse/shared/machineId.js

@@ -0,0 +1,19 @@
+import { machineIdSync } from "node-machine-id";
+import crypto from "node:crypto";
+
+let cachedRawId = null;
+
+function loadRawMachineId() {
+  if (cachedRawId) return cachedRawId;
+  try {
+    cachedRawId = machineIdSync();
+  } catch {
+    cachedRawId = crypto.randomUUID();
+  }
+  return cachedRawId;
+}
+
+export async function getConsistentMachineId(salt = "endpoint-proxy-salt") {
+  const rawId = loadRawMachineId();
+  return crypto.createHash("sha256").update(rawId + salt).digest("hex").substring(0, 16);
+}