Add evidence store, intent store and the fluid CLI

Completes FLUID-WP-0003. The evidence store is append-only at the
database, not by convention in Go: a trigger blocks UPDATE and DELETE on
fluid_events in both SQLite and Postgres, so the guarantee binds a psql
session and the CLI equally, not just callers who go through the Go API.
Records are derived summary state and may be superseded; the event log
stays the authority.

The intent store makes a recorded version immutable and content
addressed, since reassigning what governed a revision after the fact
would break the one audit question Blueprint 27 exists to answer. The
unfilled InterfaceEvolutionIntent template is rejected rather than
defaulted, because a template still listing every FLUID-N mode has not
been completed and defaulting it would pick a permissive authority by
accident.

The CLI reads the evidence store directly rather than through the
control-plane API, so an operator can reconstruct history when the
control plane is down.

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/ids.go

@@ -34,6 +34,8 @@ const (
 	KindEvent              EntityKind = "event"
 	KindFeedback           EntityKind = "feedback"
 	KindCohort             EntityKind = "cohort"
+	KindIntent             EntityKind = "intent"
+	KindRoutingPolicy      EntityKind = "routing_policy"
 )
 
 // prefixOrder matters: "BR-" must be tested before "B"-less single letters