feat(server): type REST OpenAPI contracts

Replace the generic OpenAPI request and response schemas with route-specific
components for the WorldForge REST server. This makes /v1/openapi.json useful
for client generation and contract validation while preserving runtime route
behavior.

Milestone: Typed OpenAPI contract for REST server
Changes:
- crates/worldforge-server/src/lib.rs: add reusable OpenAPI schema helpers and typed route components
- crates/worldforge-server/src/lib.rs: emit typed request-body refs and route-specific success envelopes
- crates/worldforge-server/tests/integration.rs: verify live OpenAPI request and response refs for representative POST routes
- README.md: document that /v1/openapi.json now carries typed route schemas

Validated: cargo fmt -- --check; cargo test -p worldforge-server --quiet; cargo test --workspace --quiet; cargo clippy -p worldforge-server --all-targets -- -D warnings; cargo clippy --workspace --all-targets -- -D warnings

Author: AbdelStark

README.md

@@ -829,8 +829,10 @@ Python bindings now reuse the shared Rust core facade for provider discovery,
 health checks, prediction comparison, and state persistence instead of
 duplicating orchestration logic. The REST server now also publishes a
 machine-readable `/v1/openapi.json` contract generated from the same route
-catalog that powers the `/v1` index, so the live API surface stays discoverable
-without maintaining a second hand-written route list.
+catalog that powers the `/v1` index, with typed route-specific request and
+response schemas for client generation and validation instead of a generic
+envelope-only document. The live API surface stays discoverable without
+maintaining a second hand-written route list.
 The mock provider now serves as a higher-fidelity offline reference backend:
 object motion keeps bounding boxes and inferred relationships in sync,
 predictions can emit lightweight preview video/depth/segmentation outputs, and