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/json/revision-descriptor.json

@@ -0,0 +1,35 @@
+{
+  "revision": {
+    "contract": {
+      "digest": "sha256:3b1f9c2e7a4d8b6051e2c9f0a7d4b83e15c6f2a9d0b7e4c1836a5f2d9c0b7e41",
+      "source": "artifact:openapi/customer-finance-api/r22",
+      "type": "openapi"
+    },
+    "id": "R-000221",
+    "intent": {
+      "version": "IEI-7"
+    },
+    "interface": "customer-finance-api",
+    "policy": {
+      "compatibility": "additive",
+      "policy_check": "passed",
+      "rollback_to": "R-000220",
+      "security_check": "passed"
+    },
+    "routing": {
+      "eligible_cohorts": [
+        "partner-integrations",
+        "coding-agents"
+      ],
+      "max_traffic_share": 0.3
+    },
+    "runtime": {
+      "digest": "sha256:3b1f9c2e7a4d8b6051e2c9f0a7d4b83e15c6f2a9d0b7e4c1836a5f2d9c0b7e41",
+      "image": "registry/fluid/customer-finance:R-42",
+      "timeout_ms": 5000,
+      "upstream": "http://adapter-r22.fluid-runtime.svc:8080"
+    },
+    "schema_version": "0.1",
+    "state": "candidate"
+  }
+}