[API] Stabilize Pullpiri API and Release Official v1 Specification

[Chulhee1Lee]

Description:
Currently, only a subset of Pullpiri’s API endpoints are documented, and the full specification is still marked as TBD. For OEM/Tier1 developers to integrate reliably, API version v1 should be defined with clear endpoints, request/response formats, and error-handling rules.

Proposal:

• Define and document REST/gRPC API v1
• Provide an OpenAPI/Swagger-based API portal
• Establish API versioning policy (maintain compatibility between v1/v2)