docs(http): add ADR-043 WebTransport bidirectional ALPN substrate; fix spec drift from mid-spec pivot

A consistency review of the alknet-http specs found two classes of
issues: internal contradictions from the mid-spec pivot (the to_openapi
gateway pattern landed in prose but not in cross-references), and a
systematic client→server assumption that only holds for the OpenAPI/MCP
case leaking into the WebTransport architecture.

Class 1 (internal contradictions):
- C1: to_openapi was half-refactored — body described the ADR-042
  gateway pattern but the decisions table and ADR-036 still said
  'paths mirror /{service}/{op}'. ADR-036's to_openapi clause is now
  amended as superseded by ADR-042; the stale decisions row and README
  Principle 2 are fixed.
- C2: the axum Router route list didn't include the 5 gateway endpoints
  (/search, /schema, /call, /batch, /subscribe). Added them; clarified
  /openapi.json as the gateway description doc; added gateway paths to
  the decoy exclusion list.
- C3: ADR-034 §5 still talked about the 'h3/WebTransport deferral
  bucket' that ADR-038 eliminated. Amended §5/Consequences/References
  to drop the deferral framing (the auth-model decision stands; only
  the 'when' wording was stale).

Class 2 (one-way direction assumption):
- C4/C5/C6: the WebTransport specs framed the session as browser→hub
  one-way, when the call protocol is bidirectional and WebTransport is
  a general ALPN transport substrate. New ADR-043 reframes WebTransport
  as a bidirectional ALPN transport substrate (call protocol is the
  first/canonical target; needs no WASM parser), names the call
  protocol's bidirectionality over WebTransport sessions, and states
  the inbound no-PeerId connection-local overlay as the mirror of
  ADR-034 §2. webtransport.md is updated to reflect this framing;
  ADR-040 is repositioned (not superseded) as the substrate's non-call-
  ALPN mechanism.
- C7: the HTTP/1.1+HTTP/2 surface's one-directionality is now named as
  a lossy consequence of HTTP request/response; WebTransport is named
  as the surface that restores the bidirectional call model.
- C8: overview.md acknowledges the from/to direction model is
  OpenAPI/MCP-specific, not a call-protocol property.

A review subagent pass on ADR-043 + webtransport.md found no critical
issues; warnings W1-W3 (residual browser-as-subject framing, ADR-009
rationale in spec, opening abstract tone) and suggestions S2/S4/S5
were addressed.

docs/architecture/crates/http/http-adapters.md

@@ -352,8 +352,8 @@ once published, the 5-endpoint gateway shape is one-way.
 | `from_openapi` provenance is a leaf | [ADR-022](../../decisions/022-handler-registration-provenance-and-composition-authority.md) | `composition_authority: None`, `scoped_env: None` |
 | Error fidelity (`HTTP_<status>` codes) | [ADR-023](../../decisions/023-operation-error-schemas.md) | No collision with protocol codes; `to_openapi` projects back |
 | No-env-vars credential injection | [ADR-014](../../decisions/014-secret-material-flow-and-capability-injection.md) | Handler reads `context.capabilities`, not env vars |
-| HTTP path = operation path | [ADR-036](../../decisions/036-http-to-call-operation-mapping.md) | `to_openapi` paths mirror `/{service}/{op}` |
-| `to_openapi` gateway pattern | [ADR-042](../../decisions/042-openapi-gateway-pattern.md) | 5 fixed gateway endpoints (search/schema/call/batch/subscribe), not one path per operation; per-caller AccessControl-filtered |
+| HTTP path = operation path (direct-call surface) | [ADR-036](../../decisions/036-http-to-call-operation-mapping.md) | `POST /{service}/{op}` → `call.requested` (the direct-call surface; not what `to_openapi` describes) |
+| `to_openapi` gateway pattern | [ADR-042](../../decisions/042-openapi-gateway-pattern.md) | 5 fixed gateway endpoints (search/schema/call/batch/subscribe), not one path per operation; per-caller AccessControl-filtered. Supersedes ADR-036's original `to_openapi` "paths mirror `/{service}/{op}`" clause |
 
 ## Open Questions