feat: add test suite, fix backend bugs, remove legacy artifacts 🧪

- Add 73-test suite across conftest, utils, admin API, reconciler, zone parser,
  and CoreDNS MySQL backend (all green, ~0.5s)
- Fix zone_exists filter using wrong column name (name → zone_name)
- Fix delete_zone missing dot_fqdn normalization on lookup
- Remove spurious unused `from config import config` in coredns_mysql.py
- Fix config loader to search module-relative path so tests find app.yml
  without needing a root-level config/ directory
- Remove legacy v1 Flask prototype (app.py), empty config.json, and
  duplicate root config/app.yml

directdnsonly/config/app.yml

@@ -12,8 +12,10 @@ app:
 # If a DA server is unreachable, that server is skipped entirely.
 #reconciliation:
 #  enabled: true
+#  dry_run: true             # log orphans but do NOT queue deletes — safe first-run mode
 #  interval_minutes: 60
 #  verify_ssl: true          # set false for self-signed DA certs
+#  ipp: 1000                 # items per page when polling DA (default 1000)
 #  directadmin_servers:
 #    - hostname: da1.example.com
 #      port: 2222