cli: Inject --system into bootc internals cfsctl by default

Without this, `bootc internals cfsctl oci images` (and other cfsctl
subcommands) would fall back to cfsctl's own default repo heuristic.
While cfsctl already picks /sysroot/composefs when running as root,
being explicit here documents the intent and makes the behaviour
consistent regardless of uid.  Pass --system rather than hardcoding
the path so the constant lives in one place (cfsctl's system_path()).

Users can still override with --repo, --user, or --system and the
injected flag is skipped in that case.

Assisted-by: OpenCode (claude-sonnet-4-6@default)
Signed-off-by: Colin Walters <walters@verbum.org>

Author: cgwalters

crates/lib/src/cli.rs

@@ -2086,7 +2086,25 @@ async fn run_from_opt(opt: Opt) -> Result<()> {
                     Ok(())
                 }
             },
-            InternalsOpts::Cfs { args } => composefs_ctl::run_from_iter(args.iter()).await,
+            InternalsOpts::Cfs { args } => {
+                // Inject `--system` (which resolves to /sysroot/composefs) unless the
+                // caller has already specified a repo location via --repo, --user, or
+                // --system.  This ensures `bootc internals cfsctl oci images` (and
+                // similar subcommands) operate on the booted composefs repository by
+                // default rather than falling back to cfsctl's own heuristic.
+                let has_repo_flag = args.iter().any(|a| {
+                    let s = a.to_string_lossy();
+                    s == "--repo" || s.starts_with("--repo=") || s == "--user" || s == "--system"
+                });
+                if has_repo_flag {
+                    composefs_ctl::run_from_iter(args.iter()).await
+                } else {
+                    composefs_ctl::run_from_iter(
+                        std::iter::once(OsString::from("--system")).chain(args.into_iter()),
+                    )
+                    .await
+                }
+            }
             InternalsOpts::Reboot => crate::reboot::reboot(),
             InternalsOpts::Fsck => {
                 let storage = &get_storage().await?;