docs: update CLAUDE.md with development guidance

[STRRL]

Updated CLAUDE.md with practical development commands and architecture documentation to help future Claude Code instances work more efficiently in this codebase.

Changes:

• Added build and testing commands (make build, make run, make test, make test-e2e, make lint)
• Added instructions for running single tests and Ginkgo specs
• Added comprehensive code architecture section covering CRDs, controllers, component builders, and database migrations
• Added key patterns (idempotent reconciliation, finalizers, component builder, status conditions)
• Removed outdated sections and project-management content

This document now serves as a practical reference for developers working on the Supabase Operator.