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Records are derived summary state and may be superseded; the event log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

cmd/fluid/flags.go

@@ -0,0 +1,23 @@
+package main
+
+import (
+	"flag"
+	"os"
+)
+
+// flagSet wraps flag.FlagSet so subcommands report errors instead of exiting,
+// which keeps error handling in one place in run().
+type flagSet struct{ fs *flag.FlagSet }
+
+func newStdFlagSet(name string) *flag.FlagSet {
+	fs := flag.NewFlagSet(name, flag.ContinueOnError)
+	fs.SetOutput(os.Stderr)
+	return fs
+}
+
+func (f *flagSet) String(name, value, usage string) *string { return f.fs.String(name, value, usage) }
+func (f *flagSet) Bool(name string, value bool, usage string) *bool {
+	return f.fs.Bool(name, value, usage)
+}
+func (f *flagSet) Int(name string, value int, usage string) *int { return f.fs.Int(name, value, usage) }
+func (f *flagSet) Parse(args []string) error                     { return f.fs.Parse(args) }