[codex] Fix local daemon auto-connect for test-support wrappers

[svarlamov]

Summary

• allow locally run test-support wrappers to auto-connect to the daemon when they are not running under the integration harness
• preserve wrapper-daemon test behavior by continuing to honor explicit daemon socket env vars first and by skipping auto-connect when the existing test DB env markers are present
• add unit coverage for test-harness detection and explicit socket override precedence

Root Cause

init_daemon_telemetry_handle() treated every test-support build as a harness-managed test binary. In local dev, that meant the wrapper skipped daemon auto-connect unless GIT_AI_DAEMON_CONTROL_SOCKET was set, leaving the telemetry handle disconnected and producing noisy failed to send pre/post-state messages even though the daemon fallback path still worked.

Validation

• cargo test test_harness_detection_uses_test_db_override_vars -- --nocapture
• cargo test --lib explicit_control_socket_override_wins_over_test_harness_marker -- --nocapture
• cargo build --bin git-ai --features test-support
• manual repro: exec -a git target/debug/git-ai add a.txt in a temp repo without daemon socket env vars; wrapper warning no longer appears