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/telemetry-envelope.json

@@ -0,0 +1,34 @@
+{
+  "fluid_telemetry": {
+    "cohort": "coding-agents",
+    "consumer_ref": "psu-4d1e9c",
+    "correlation_id": "c-7f21ab90",
+    "experiment": "E-000093",
+    "id": "tl-01J8Z3XK7QW2",
+    "interface_id": "customer-finance-api",
+    "kind": "request",
+    "occurred_at": "2026-09-05T08:14:22Z",
+    "redaction": {
+      "applied": true,
+      "rules": [
+        "drop-path-parameters",
+        "pseudonymize-consumer"
+      ]
+    },
+    "request": {
+      "latency_ms": 118.4,
+      "method": "GET",
+      "operation": "getLatestInvoice",
+      "request_bytes": 0,
+      "response_bytes": 812,
+      "route": "/customers/{id}/invoices/latest",
+      "status": 200
+    },
+    "resolution": {
+      "policy_generation": 118,
+      "reason": "experiment_assignment"
+    },
+    "revision": "R-000221",
+    "schema_version": "0.1"
+  }
+}