v0.7.0

v0.7.0 — generator coverage + richer error typing

v0.7.0 widens what wavefront expresses on both ends of the contract. The
generator bundles a broader range of real FastAPI/OpenAPI surfaces — empty
objects, typed and open dictionaries, and polymorphic unions — and the proxy
stops collapsing every non-success into one envelope: a declared (route, status)
is now a typed, status-preserving contract response. Generator output stays
byte-reproducible — the well-known-type descriptors are embedded in a layer only
when a schema actually uses them.

• Empty object schemas bundle as zero-field messages. A component that is an
  explicitly-empty object ({"type":"object","properties":{}}) — the shape
  FastAPI emits for a fieldless model — bundles as a zero-field proto message
  instead of being rejected. A bare {"type":"object"} with no properties key is
  still a hard error, the open/untyped-object boundary (#118 closed).

• Typed additionalProperties lowers to a proto3 map. A typed dictionary
  (additionalProperties: <scalar|$ref>, no declared properties of its own)
  lowers to map<string, V> (#119 closed).

• Open objects and untagged unions lower to well-known types. An open object
  (additionalProperties: true | {}) lowers to google.protobuf.Struct; an untagged
  anyOf/oneOf union or an unconstrained {} schema lowers to google.protobuf.Value
  (repeated as array items). google/protobuf/struct.proto is embedded in the
  layer only when used, so bundles that need neither stay byte-identical. This
  types FastAPI's HTTPValidationError.loc: list[str | int] (#121).

• Discriminated unions lower to Struct. A tagged anyOf/oneOf (one carrying a
  discriminator) serializes flattened — the discriminator is a sibling property
  and the member's fields sit at the top level — which a proto3 oneof cannot
  carry (protojson encodes a oneof wrapped under the member key). It lowers to
  google.protobuf.Struct, which relays the object verbatim (#129 closed).

• Upstream-origin status codes and typed error bodies. wavefront no longer
  collapses every non-success to a fixed wavefront.v0.Error envelope. A declared
  (route, status) is a first-class typed contract response: the upstream status
  is preserved and no X-Wavefront-Error header is set. Undeclared statuses fall
  to the graceful aid envelope. wavefront honors whatever status the upstream
  sends except a hard capability ceiling — 206/207/208/226 and any 3xx map to
  502. A per-route strict: true flips the undeclared-status default to a hard
  502. resolution.yaml field transforms (rename/default/optionalize/coerce) fire
  per (status, message) pair, not only on 2xx (#53 closed).

• fix: accept empty object schemas as zero-field messages (#122)

• feat: lower a typed-dict additionalProperties to map<string,V> (#123)

• feat: bind per-status error_messages and strict in the bundle loader (#124)

• feat: collect and bind declared error response types in the generator (#125)

• feat: honor upstream status, type declared errors, relay the rest (#126)

• feat: apply field transforms per declared error status (#127)

• test: exercise per-status error transforms across a version chain (#128)

• feat: lower untagged unions and open objects to well-known types (#130)

• feat: lower discriminated unions to google.protobuf.Struct (#131)