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/global_defaults/tasks/system.yml

@@ -114,6 +114,9 @@
               else []
             )
           }}
+      timezone: "{{ system_raw.timezone | default('Europe/Vienna') | string }}"
+      locale: "{{ system_raw.locale | default('en_US.UTF-8') | string }}"
+      keymap: "{{ system_raw.keymap | default('us') | string }}"
       path: "{{ system_raw.path | default('') | string }}"
       packages: >-
         {{