docs(claude): condense CLAUDE.md from 964 to 554 lines (43% reduction)

- Condense OAuth Callback Stub section (117 → 25 lines)
- Condense Client Credentials Grant section (159 → 21 lines)
- Condense WebSocket Test Harness section (59 → 12 lines)
- Condense CATS API Fuzzing section (48 → 12 lines)
- Condense Arazzo Workflow section (33 → 7 lines)
- Trim SBOM Generation and Container Base Images sections
- Merge redundant testing sections (Testing Commands, Test Execution
  Guidelines, Test Philosophy) into single consolidated section
- Remove duplicate Public Endpoints documentation
- File reduced from 44KB to 25KB

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: ericfitz