Add two test files covering the delivery-mode and workspace-status
enforcement contracts:
- models/workspace_delivery_mode_test.go:
- IsValidDeliveryMode: true for "push"/"poll", false for all
other inputs (empty, typos, case variants, trailing space)
- WorkspaceStatus.String(): returns the underlying string for all 10
status constants
- AllWorkspaceStatuses: correct length (10) and membership of all
named constants, no empty strings
- handlers/workspace_dispatchers_test.go:
- resolveDeliveryMode: payloadMode wins without DB query, existing
DB mode returned when present, external runtime defaults to poll,
self-hosted defaults to push, not-found defaults to push,
DB errors propagate, empty-string existing mode falls through
to runtime check
Refs #860
