fix(agents-init): quiet only on change, add -v/--verbose flag

- quiet mode now outputs one summary line only when something actually changed;
  idempotent re-runs produce no output
- add -v/--verbose flag as an explicit alias for the default verbose behavior
- gitignore helper output captured to detect changes without printing in quiet mode
- drop eager "Initializing…" header in favour of end-of-run conditional summary

.gitignore

@@ -288,3 +288,8 @@ poetry.toml
 pyrightconfig.json
 
 # End of https://www.toptal.com/developers/gitignore/api/python
+
+#   ──────────────── Added by agents-init ──────────────────
+#   agents-init --agents
+AGENTS/
+#   ────────────────────────────────────────────────────────