Add science control APIs and the hypothesis, experiment and promote CLI

Completes FLUID-WP-0006. The loop now runs end to end from the command
line: two competing presentation hypotheses, an experiment that issues a
routing policy rather than touching traffic, an amendment, a stop that
returns traffic to the default, a confirmed outcome, a resolved
competition, and a promotion the gate can refuse.

Starting or stopping an experiment returns the routing policy for the
operator to install rather than installing it. Blueprint 17 keeps the
controller out of the traffic path, and installing from the handler
would put it straight back in; emitting the document keeps the
separation visible instead of implied.

`fluid audit trace` now answers the section 25 questions from events
rather than summary records, and names the rivals a hypothesis beat: an
audit asking which hypotheses were considered is not answered by naming
only the winner.

Two fixes found by driving the CLI rather than only the tests. Go's flag
package stops at the first positional, so ids given after flags silently
swallowed them; ids are now taken before parsing. And there was no way
to attach a revision to the hypothesis that produced it, which left
`audit trace` unable to say why a revision existed -- `hypothesis attach`
closes that.

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/main.go

@@ -35,6 +35,9 @@ Commands:
   pressure dismiss Record that a pressure will not be acted on
   cohort           Summarize cohort populations
   fitness compare  Compare a candidate revision against its control
+  hypothesis       Create, advance and compete hypotheses
+  experiment       Design, start, stop and finalize experiments
+  promote          Record a promotion decision
   events           Show audit events
   telemetry        Show recorded telemetry
   audit trace      Reconstruct the history behind a revision
@@ -124,6 +127,12 @@ func run(args []string) error {
 		return runCohort(ctx, g, rest)
 	case "fitness":
 		return runFitness(ctx, g, rest)
+	case "hypothesis":
+		return runHypothesis(ctx, g, rest)
+	case "experiment":
+		return runExperiment(ctx, g, rest)
+	case "promote":
+		return runPromote(ctx, g, rest)
 	case "audit":
 		return runAudit(ctx, g, rest)
 	default: