fix: preserve resolved prompt permissions

[kocaemre]

Summary

• Preserve the Codex app-server's resolved default approval/reviewer/sandbox settings in session metadata.
• Use those resolved permissions for default Agent prompts instead of reapplying the hardcoded default Agent preset.
• Keep explicit non-default mode behavior unchanged, and continue adding ACP additionalDirectories to workspace-write roots.
• Add regression coverage for configured writable roots/network access and explicit mode overrides.

Closes #477

Test Plan

• npm run typecheck
• npx vitest run src/__tests__/CodexACPAgent/CodexAcpClient.test.ts --testNamePattern 'preserves resolved default prompt permissions|uses explicit non-default mode prompt permissions|applies ACP additional directories'
• npx vitest run src/__tests__/CodexACPAgent/CodexAcpClient.test.ts
• git diff --check

Note: the full targeted test file prints existing stderr log lines from auth/rate-limit negative-path tests, but the Vitest run exited successfully with 107/107 tests passing.