Add channel-level Bedrock CC compatibility toggle (similar to web_search_emulation)
that fixes 4 types of Bedrock 400 errors seen with Claude Code:
1. thinking.type "enabled" → "adaptive" for Opus 4.7+ (only supports adaptive)
2. Add default budget_tokens when missing for older models
3. Replace illegal characters in tool_use IDs to match Bedrock's ^[a-zA-Z0-9_-]+$ pattern
4. anthropic_version / invalid beta flag (already handled elsewhere)
Transformations run in Forward() before any forwarding path, so both native Bedrock
accounts and apikey passthrough accounts pointing to Bedrock relays benefit.
Includes channel-level toggle UI and unit tests.
4fd21994c5