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Records are derived summary state and may be superseded; the event log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

workplans/FLUID-WP-0003-deterministic-data-plane.md

@@ -113,7 +113,7 @@ backpressure must never block or slow a request. Test it under a stalled sink.
 
 ```task
 id: FLUID-WP-0003-T08
-status: todo
+status: done
 priority: high
 state_hub_task_id: "1773c7bf-9400-576e-9e74-aa210f08e0c4"
 ```
@@ -125,7 +125,7 @@ summaries exist only as derived views (§26).
 
 ```task
 id: FLUID-WP-0003-T09
-status: todo
+status: done
 priority: high
 state_hub_task_id: "23d70a60-14bf-525e-a712-1d3a14111f62"
 ```
@@ -138,7 +138,7 @@ was made.
 
 ```task
 id: FLUID-WP-0003-T10
-status: todo
+status: done
 priority: medium
 state_hub_task_id: "ad7d83d7-a088-5ea4-94e7-fa5be49897b9"
 ```