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/feedback.yaml

@@ -0,0 +1,22 @@
+fluid_feedback:
+  schema_version: "0.1"
+
+  id: "F-9821"
+  interface_id: "customer-finance-api"
+  received_at: "2026-08-28T09:12:00Z"
+  cohort: "coding-agents"
+  revision: "R-000220"
+
+  goal: "produce monthly account statement"
+  missing_capability: "consolidated-period-summary"
+  attempted_operations:
+    - "list-transactions"
+    - "get-balances"
+  outcome: "capability unavailable"
+  workaround:
+    - "aggregate-locally"
+    - "infer-closing-balance"
+  confidence: 0.94
+  impact:
+    calls: 18
+    latency_ms: 2810