check: compile and validate the access policy; --access prints the matrix

Every check now compiles the content into portal's Cedar policy and
fails when it does not validate against the schema - a rule the
schema cannot express would grant nothing at runtime. `--access`
prints the matrix: action, resource, who, and the state move where it
applies. Pinned to portal v0.3.40, where the policy lives.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01L4jrCgLiKKHAEFuZUJjckH

src/main.rs

@@ -44,7 +44,7 @@ async fn main() -> anyhow::Result<()> {
         Some(flag) if flag.starts_with("--") => check::run(argv).await,
         _ => {
             eprintln!(
-                "iris {v} - matches portal v{v}\n\nusage:\n  iris check (--repo <gitea-url> [--branch main] [--subdir questions] | --path <dir>) [--needs-tasks <out.jsonl> [--skim]] [--needs-sim <model.json>] [--needs-score <answers.jsonl> [--min-accuracy 0.8]]\n  iris replay --path <dir> --nats <url> (--cases <cases.jsonl> | --report-only)",
+                "iris {v} - matches portal v{v}\n\nusage:\n  iris check (--repo <gitea-url> [--branch main] [--subdir questions] | --path <dir>) [--needs-tasks <out.jsonl> [--skim]] [--needs-sim <model.json>] [--access] [--needs-score <answers.jsonl> [--min-accuracy 0.8]]\n  iris replay --path <dir> --nats <url> (--cases <cases.jsonl> | --report-only)",
                 v = env!("CARGO_PKG_VERSION")
             );
             std::process::exit(2)