Fix OpenAPI Spec Mismatches vs Actual Responses/Status Codes

Summary

Fixed critical mismatches between the OpenAPI specification and actual API implementation to ensure accurate client expectations and documentation.

Response Envelope Structure: Updated all response schemas to reflect the actual standardized envelope pattern:
- Success responses: { success: true, data: {...}, meta: { timestamp, requestId? } }
- Error responses: { success: false, error: { code, message, details?, requestId? } }
Removed Unimplemented Endpoints: Removed all webhook-related endpoints that are not yet implemented
Updated Status Codes: Removed 422 status code (implementation uses 400 for validation errors)
Fixed Response Schemas:
- Created StreamResponse, StreamListResponse, CancelStreamResponse schemas that wrap data in envelope
- Created HealthResponse, ReadinessResponse, LivenessResponse for health endpoints
- Updated ErrorResponse schema to match actual error envelope structure
Added Health Endpoints: Documented /health/ready and /health/live endpoints
Fixed Stream ID Format: Updated documentation to reflect actual format stream-{timestamp}-{random}

Added import for successResponse from ../utils/response.js
Added imports for validation helpers: parseBody, formatZodIssues, CreateStreamSchema
Added imports for stream status helpers: assertValidApiTransition, ApiStreamStatus

Corrected errorResponse() function calls to use correct parameter order: (code, message, details?, requestId?)
Fixed /health/ready endpoint error responses
Fixed /health/live endpoint error responses

Updated all success response assertions to access data via response.body.data instead of response.body
Updated POST /api/streams tests to check response.body.data.id, response.body.data.depositAmount, etc.
Updated GET /api/streams tests to check response.body.data.streams, response.body.data.has_more, etc.
Maintained error response assertions (already at top level)