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

internal/contract/feedback_gen.go

@@ -0,0 +1,33 @@
+// Code generated by tools/schemagen. DO NOT EDIT.
+// Source: schemas/. Regenerate with `make generate`.
+
+package contract
+
+type FluidFeedbackImpact struct {
+	Calls       *int64   `json:"calls,omitempty" yaml:"calls,omitempty"`
+	Description string   `json:"description,omitempty" yaml:"description,omitempty"`
+	LatencyMS   *float64 `json:"latency_ms,omitempty" yaml:"latency_ms,omitempty"`
+}
+
+type FluidFeedback struct {
+	Attempt             string               `json:"attempt,omitempty" yaml:"attempt,omitempty"`
+	AttemptedOperations []string             `json:"attempted_operations,omitempty" yaml:"attempted_operations,omitempty"`
+	Cohort              *CohortID            `json:"cohort,omitempty" yaml:"cohort,omitempty"`
+	Confidence          *UnitInterval        `json:"confidence,omitempty" yaml:"confidence,omitempty"`
+	Goal                string               `json:"goal" yaml:"goal"`
+	ID                  FeedbackID           `json:"id" yaml:"id"`
+	Impact              *FluidFeedbackImpact `json:"impact,omitempty" yaml:"impact,omitempty"`
+	InterfaceID         InterfaceID          `json:"interface_id" yaml:"interface_id"`
+	MissingCapability   string               `json:"missing_capability,omitempty" yaml:"missing_capability,omitempty"`
+	Outcome             string               `json:"outcome,omitempty" yaml:"outcome,omitempty"`
+	ReceivedAt          Timestamp            `json:"received_at" yaml:"received_at"`
+	Revision            *RevisionID          `json:"revision,omitempty" yaml:"revision,omitempty"`
+	SchemaVersion       SchemaVersion        `json:"schema_version" yaml:"schema_version"`
+	Workaround          any                  `json:"workaround,omitempty" yaml:"workaround,omitempty"`
+}
+
+// Structured feedback from a consumer. Treated as evidence and never as authority
+// to change anything (FluidAPIStandards.md section 15).
+type FeedbackDocument struct {
+	FluidFeedback FluidFeedback `json:"fluid_feedback" yaml:"fluid_feedback"`
+}