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/activity/mod.rs

@@ -55,7 +55,17 @@ fn log_path() -> PathBuf {
 /// the Activity tab's commit feed (sourced straight from git log) covers
 /// separately and accurately regardless of how it happened.
 pub fn log(entry: &ActivityEntry) {
-    let Ok(line) = serde_json::to_string(entry) else { return };
+    // Executor marker: AI agents set VULP_AGENT so their actions are
+    // distinguishable from the human's in the shared log.
+    let mut entry = entry.clone();
+    if std::env::var("VULP_AGENT").map(|v| !v.is_empty()).unwrap_or(false) {
+        entry.detail = if entry.detail.is_empty() {
+            "via agent".into()
+        } else {
+            format!("{} · via agent", entry.detail)
+        };
+    }
+    let Ok(line) = serde_json::to_string(&entry) else { return };
     let path = log_path();
     if let Some(parent) = path.parent() {
         let _ = std::fs::create_dir_all(parent);