Generate contract types, pin fixtures to spec, add build and ADRs

Completes FLUID-WP-0002. The record types in internal/contract are
generated from schemas/ by a dependency-free generator; fixtures
transcribed from the spec's worked examples validate against those
schemas and round-trip through the generated types with
DisallowUnknownFields, so a spec change that misses the schemas fails
CI rather than drifting silently.

Adds identifier prefix helpers, Makefile, GitHub Actions, and five ADRs
recording the Go choice, out-of-process attachment, the wire contract as
boundary, the evidence store, and revision identity.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014KmVxhJ35tCo7rE7UnLwWu

Assistant: claude-code
Assistant-Model: opus
Assistant-Process: 1116572@bnt-lap001
Assistant-Session: 8ba9bb93-a72a-4883-b189-2499cce5c400

docs/adr/0002-out-of-process-attachment.md

@@ -0,0 +1,43 @@
+# ADR-0002 — Out-of-process attachment
+
+**Status:** accepted · **Date:** 2026-09-04
+
+## Context
+
+A FLUID interface has to be able to wrap an existing API. The question is
+whether fluid-core is a library that API imports, or a process that sits in
+front of it.
+
+Blueprint §42 already answers this implicitly: `gateway`, `revision-router` and
+`adapter-r41`/`adapter-r42` are separate deployments. That is process-level
+integration, not library-level.
+
+## Decision
+
+fluid-core attaches out of process. The gateway and router run in front of
+adapter processes reached over the network. The target API contributes no code,
+imports no library, and may be written in any stack.
+
+An in-process SDK is explicitly deferred, not rejected. It would buy richer
+signal — call-sequence correlation and structured consumer feedback that a
+proxy cannot see from outside — at the cost of SDK versioning across languages.
+
+## Rationale
+
+Minimal conformance (`FluidAPIStandards.md` §36) requires a deterministic
+contract, revision identity, telemetry, declared intent, an evidence link,
+responsibility boundaries and deterministic security. Every one of those is
+observable from the proxy. Nothing in the conformance core needs to be inside
+the target process.
+
+The language-agnostic promise is only credible if the framework never asks for
+an import. Making the SDK optional from the start, rather than retrofitting the
+proxy later, is what keeps that true.
+
+## Consequences
+
+- The revision descriptor carries `runtime.upstream`: the adapter's address.
+- Interaction topology (Blueprint §6.4) is reconstructed from correlation IDs
+  observed at the gateway, not reported by the consumer.
+- Explicit feedback (`FluidAPIStandards.md` §15) arrives over the wire as its
+  own endpoint rather than through an SDK call.