refactor(bootstrap): standardize patterns, extract common logic, remove dead code

- Make timezone, locale, and keymap configurable via system_cfg
- Consolidate rhel8/9/10.repo.j2 into single rhel.repo.j2 template
- Extract bootstrap_common_conditional for shared firewall/LUKS/guest packages
- Remove redundant version aliases (fedora40-43, debian10-13, rhel8-10, etc.)
- Simplify bootstrap dispatch from 10 conditional blocks to single mapping
- Merge bootstrap_ubuntu_lts into bootstrap_ubuntu (identical)
- Remove orphaned firstrun.sh.j2 template
- Remove configuration/defaults/main.yml aliases, inline into banner.yml
- Remove unnecessary changed_when: false on set_fact/debug tasks
- Deduplicate hostname variable computation in locales.yml
- Update README with timezone/locale/keymap variable reference

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

roles/configuration/tasks/banner.yml

@@ -1,6 +1,6 @@
 ---
 - name: Configure MOTD
-  when: configuration_motd_enabled | bool
+  when: system_cfg.features.banner.motd | bool
   block:
     - name: Create MOTD file
       ansible.builtin.copy:
@@ -24,7 +24,7 @@
       failed_when: false
 
 - name: Configure sudo banner
-  when: configuration_sudo_banner_enabled | bool
+  when: system_cfg.features.banner.sudo | bool
   block:
     - name: Create sudoers banner directory
       ansible.builtin.file: