fix(test): narrow mock.module() targets in background-agent tests to prevent barrel corruption

Three test files were mocking the entire '../../shared' barrel, which
corrupted exports for subsequent test files in the same batch run.
Narrow mocks to specific submodules (logger, connected-providers-cache).

Also reverts Bun version pin since the root cause was mock scope, not Bun.

src/features/background-agent/abort-with-timeout.test.ts

@@ -2,7 +2,7 @@ import { afterAll, describe, expect, mock, test } from "bun:test"
 
 const logMock = mock(() => {})
 
-mock.module("../../shared", () => ({
+mock.module("../../shared/logger", () => ({
   log: logMock,
 }))