Refactor DNS handling and add solo record support

- Added 'solo' flag support for A/AAAA, CNAME/MX/TXT, and SRV records in sys-dns-cloudflare-records.
- Simplified sys-svc-dns: removed NS management tasks and CLOUDFLARE_NAMESERVERS default.
- Renamed 03_apex.yml back to 02_apex.yml, adjusted AAAA task name.
- Updated web-app-bluesky DNS tasks: marked critical records with 'solo'.
- Updated web-app-mailu DNS tasks: removed cleanup block, enforced 'solo' on all records.
- Adjusted constructor stage to call domain_mappings with AUTO_BUILD_ALIASES parameter.

Conversation: https://chatgpt.com/share/68cd20d8-9ba8-800f-b070-f7294f072c40

tasks/stages/01_constructor.yml

@@ -76,7 +76,7 @@
       redirect_domain_mappings: >-
         {{ 
           CURRENT_PLAY_APPLICATIONS |
-          domain_mappings(PRIMARY_DOMAIN) | 
+          domain_mappings(PRIMARY_DOMAIN, AUTO_BUILD_ALIASES) |
           merge_mapping(redirect_domain_mappings, 'source') 
         }}