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/bootstrap/tasks/ubuntu.yml

@@ -2,7 +2,7 @@
 - name: Bootstrap Ubuntu System
   vars:
     bootstrap_ubuntu_release: >-
-      {{ 'plucky' if bootstrap_os_key == 'ubuntu' else 'noble' }}
+      {{ 'plucky' if os == 'ubuntu' else 'noble' }}
     bootstrap_ubuntu_package_config: >-
       {{
         lookup('vars', bootstrap_var_key)