fix(discord): preserve native semantic thread renames

[taikit]

Summary

• pass relay-only thread rename keywords only on the relay lane
• preserve the native Discord adapter’s only_if_current_name no-clobber contract
• surface unexpected rename failures at WARNING without logging exception messages or tracebacks
• add behavior-level regression coverage for native, relay, and failure-observability paths

Root cause

The shared gateway call passed prefer_connector_created and parent_chat_id to the native Discord adapter, whose rename_thread method does not accept those relay-only keywords. Python raised TypeError before the adapter ran, and the broad handler logged only at DEBUG, so semantic title generation appeared successful while Discord remained unchanged.

Verification

• scripts/run_tests.sh tests/gateway/test_discord_semantic_thread_rename_contract.py tests/gateway/test_session_title_rename_lane.py tests/gateway/relay/test_relay_threads.py -q — 23 passed
• ruff check gateway/run.py tests/gateway/test_discord_semantic_thread_rename_contract.py — passed
• git diff --check — passed
• independent review — passed after changing to lane-specific kwargs and removing exception text/tracebacks from warning logs

[alt-glitch]

This was generated by AI during triage.

Related to #78495: both repair the native Discord semantic-rename signature mismatch, but this PR keeps relay-only kwargs in the relay lane while #78495 expands the native adapter signature. Maintainer choice needed.