feat(api): add API versioning strategy

[martsokha]

Context

No API versioning strategy is in place. The runtime's DEVELOPER.md explicitly calls for documented deprecation timelines.

Requirements

• URI-based versioning (e.g., /v1/workspaces/)
• Breaking changes require a major version increment
• Documented deprecation timeline and migration period for old versions
• Non-breaking additions (new fields, new endpoints) within the current version
• Version negotiation documented in OpenAPI spec

References

• Server docs: ARCHITECTURE.md - API Design
• Runtime: DEVELOPER.md Section 2.1