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>

templates/rhel.repo.j2

@@ -0,0 +1,13 @@
+[rhel{{ os_version_major }}-baseos]
+name=RHEL {{ os_version_major }} BaseOS
+baseurl=file:///usr/local/install/redhat/dvd/BaseOS
+enabled=1
+gpgcheck=0
+gpgkey=file:///usr/local/install/redhat/dvd/RPM-GPG-KEY-redhat-release
+
+[rhel{{ os_version_major }}-appstream]
+name=RHEL {{ os_version_major }} AppStream
+baseurl=file:///usr/local/install/redhat/dvd/AppStream
+enabled=1
+gpgcheck=0
+gpgkey=file:///usr/local/install/redhat/dvd/RPM-GPG-KEY-redhat-release