fix(feishu): resolve canonical agent bindings

[GatewayJ]

Summary

• resolve existing Feishu workers by runtime ID or exact display name
• resolve the Manager Feishu configuration through its canonical Agent binding
• render successful Feishu setup as a concise user-facing confirmation

Validation

• go test ./...
• go test ./internal/channel/feishu ./internal/channel/feishu/participantprovider
• make build-server-bin