chore: including new clean-code inspired CLAUDE.md and moving sidecar client

[bdchatham]

Summary

• Moved the sei-sidecar-client-go API client into seictl at sidecar/client/, consolidating the sidecar HTTP client and its OpenAPI spec into the same repo as the sidecar server.
• Separated API artifacts (openapi.yaml, codegen.yaml, generate.go) into sidecar/api/ from the hand-written client wrappers in sidecar/client/.
• Updated sei-k8s-controller imports from github.com/sei-protocol/sei-sidecar-client-go to github.com/sei-protocol/seictl/sidecar/client.
• Removed sei-sidecar-client-go from go.work.
• Added CLAUDE.md with project conventions emphasizing self-documenting code over narration comments.
• Added make generate target for OpenAPI client regeneration.