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

@@ -1,12 +1,12 @@
-[rhel10-baseos]
-name=RHEL 10 BaseOS
+[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
 
-[rhel10-appstream]
-name=RHEL 10 AppStream
+[rhel{{ os_version_major }}-appstream]
+name=RHEL {{ os_version_major }} AppStream
 baseurl=file:///usr/local/install/redhat/dvd/AppStream
 enabled=1
 gpgcheck=0

templates/rhel8.repo.j2

@@ -1,13 +0,0 @@
-[rhel8-baseos]
-name=RHEL 8 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
-
-[rhel8-appstream]
-name=RHEL 8 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

templates/rhel9.repo.j2

@@ -1,13 +0,0 @@
-[rhel9-baseos]
-name=RHEL 9 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
-
-[rhel9-appstream]
-name=RHEL 9 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