feat(core): add bounded key creation contract

Expose create_redis_value through the Tauri bridge, add NX-based string creation in redis-core, and surface duplicate-key handling through stable operator notices.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

apps/desktop/src/lib/operator-notices.test.ts

@@ -65,6 +65,28 @@ describe("operator notices", () => {
     );
   });
 
+  it("maps duplicate key creation into a stable neutral notice", () => {
+    expect(
+      toBackendErrorNotice(
+        {
+          code: "already_exists",
+          message: "Redis key creation does not overwrite an existing key.",
+          detail: "key `draft:key` already exists",
+        },
+        {
+          operation: "key_create",
+          connectionName: "redis-local-fixture",
+          databaseLabel: "db0",
+          keyName: "draft:key",
+        },
+      ),
+    ).toEqual(
+      createNeutralNotice(
+        "Redis refused to proceed while creating draft:key on redis-local-fixture / db0 because the key already exists. Choose a new key name or inspect the existing key before retrying. Backend detail: Redis key creation does not overwrite an existing key. (key `draft:key` already exists).",
+      ),
+    );
+  });
+
   it("describes command failures with command and scope context", () => {
     expect(
       toBackendErrorNotice(