self-scan: allow cargo_crate in composit's own Compositfile

Composit is itself a Rust crate, so the new cargo_manifest scanner
now detects its own Cargo.toml as `cargo_crate`. With allowlist mode
(any unlisted type → resource_type_not_allowed Error), the CI
self-scan gate would block on the next push. Add an explicit
`allow "cargo_crate" { max = 2 }` block.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: 7schmiede

Compositfile

@@ -53,6 +53,11 @@ workspace "composit" {
       max = 2
     }
 
+    # The CLI is itself a Rust crate — own Cargo.toml.
+    allow "cargo_crate" {
+      max = 2
+    }
+
     # CI is mandatory. If ci.yml disappears from a PR, `composit diff --strict`
     # fails and the PR cannot merge.
     require "workflow" {