Fix BUG-001: resolve banaction interpolation error in fail2ban jails

The container init script (init-fail2ban-config) copies jail.conf from the
image's /defaults/ on every start, overwriting any direct edits.  The correct
fix is jail.local, which is not present in the image defaults and therefore
persists across restarts.

Changes:
- Add Docker/fail2ban-dev-config/fail2ban/jail.local with [DEFAULT] overrides
  for banaction = iptables-multiport and banaction_allports = iptables-allports.
  fail2ban loads jail.local after jail.conf so these values are available to
  all jails during %(action_)s interpolation.
- Untrack jail.local from .gitignore so it is committed to the repo.
- Fix TypeError in config_file_service: except jail_service.JailNotFoundError
  failed when jail_service was mocked in tests because MagicMock attributes are
  not BaseException subclasses.  Import JailNotFoundError directly instead.
- Mark BUG-001 as Done in Tasks.md.

Docker/fail2ban-dev-config/fail2ban/jail.local

@@ -0,0 +1,6 @@
+# Local overrides — not overwritten by the container init script.
+# Provides banaction so all jails can resolve %(action_)s interpolation.
+
+[DEFAULT]
+banaction = iptables-multiport
+banaction_allports = iptables-allports