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

conformance/fixtures/revision-descriptor.yaml

@@ -0,0 +1,32 @@
+revision:
+  schema_version: "0.1"
+
+  id: "R-000221"
+  interface: "customer-finance-api"
+  state: "candidate"
+
+  contract:
+    type: "openapi"
+    digest: "sha256:3b1f9c2e7a4d8b6051e2c9f0a7d4b83e15c6f2a9d0b7e4c1836a5f2d9c0b7e41"
+    source: "artifact:openapi/customer-finance-api/r22"
+
+  runtime:
+    upstream: "http://adapter-r22.fluid-runtime.svc:8080"
+    image: "registry/fluid/customer-finance:R-42"
+    digest: "sha256:3b1f9c2e7a4d8b6051e2c9f0a7d4b83e15c6f2a9d0b7e4c1836a5f2d9c0b7e41"
+    timeout_ms: 5000
+
+  intent:
+    version: "IEI-7"
+
+  routing:
+    eligible_cohorts:
+      - "partner-integrations"
+      - "coding-agents"
+    max_traffic_share: 0.30
+
+  policy:
+    compatibility: "additive"
+    security_check: "passed"
+    policy_check: "passed"
+    rollback_to: "R-000220"