Sprint B.6: CLI guardrails — --dry-run, protected_repos, VULP_AGENT marker

- global --dry-run: sync/release/init/collab/license print 'DRY RUN: would...'
  and exit 0 (no auth needed for previews where possible)
- config protected_repos (name/basename, case-insensitive): mutating commands
  exit 1 on listed repos unless --force; checked before dry-run
- VULP_AGENT env: activity::log centrally appends '· via agent' to detail,
  covering both CLI and TUI writers
- sync: unknown --action now rejected before touching any repo

src/app.rs

@@ -22,6 +22,9 @@ pub async fn run(cli: Cli) -> Result<()> {
         Some(Commands::Auth(args)) => crate::auth::run(args, &cfg).await,
 
         // ── everything else: non-interactive CLI ──
-        Some(cmd) => crate::cli_cmds::run(cmd, cli.json, &cfg).await,
+        Some(cmd) => {
+            let guard = crate::cli_cmds::Guard { dry_run: cli.dry_run, force: cli.force };
+            crate::cli_cmds::run(cmd, cli.json, guard, &cfg).await
+        }
     }
 }