Add coverage for skill lock release and fix WebRTC test flakiness (#16846)

* test: add coverage for skill lock release and simplify WebRTC test

- Add test for cleanupReleasedSkillInstallLock handling rmdir races
- Improve error handling to cover all documented directory removal error codes
- Simplify WebRTC egress test to use localhost addresses consistently

* test: use network interface address for WebRTC egress probe

- Discover the first non-internal IPv4 address instead of hardcoding
  localhost, allowing the test to work in CI and varied environments
- Update proxy rules to use loopback designation for clarity
- Bind UDP socket to all interfaces (0.0.0.0) to receive on the
  discovered address

src/main/runtime/runtime-rpc-mobile-method-allowlist.test.ts

@@ -479,7 +479,6 @@ describe('OrcaRuntimeRpcServer', () => {
       deviceToken: mobile.token,
       params: { worktree: 'id:wt-1', page: 'page-1' }
     })
-
     expect(replies).toContainEqual(
       expect.objectContaining({
         id: 'req_forbidden',