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/environment/tasks/main.yml

@@ -163,7 +163,7 @@
         - name: Setup Pacman
           when:
             - not (custom_iso | bool)
-            - item.os is not defined or (os_resolved | default(os)) in item.os
+            - item.os is not defined or os in item.os
           community.general.pacman:
             update_cache: true
             force: true
@@ -171,9 +171,9 @@
             state: latest
           loop:
             - { name: glibc }
-            - { name: dnf, os: [almalinux8, almalinux9, almalinux10, fedora40, fedora41, fedora42, fedora43, rhel8, rhel9, rhel10, rocky8, rocky9, rocky10] }
-            - { name: debootstrap, os: [debian10, debian11, debian12, debian13, debianunstable, ubuntu, ubuntu-lts] }
-            - { name: debian-archive-keyring, os: [debian10, debian11, debian12, debian13, debianunstable] }
+            - { name: dnf, os: [almalinux, fedora, rhel, rocky] }
+            - { name: debootstrap, os: [debian, ubuntu, ubuntu-lts] }
+            - { name: debian-archive-keyring, os: [debian] }
             - { name: ubuntu-keyring, os: [ubuntu, ubuntu-lts] }
           retries: 4
           delay: 15
@@ -210,12 +210,7 @@
           block:
             - name: Select repository template
               ansible.builtin.set_fact:
-                environment_repo_template: >-
-                  {{
-                    (os_resolved | default(os)) | lower
-                    if os == 'rhel'
-                    else os | lower
-                  }}
+                environment_repo_template: "{{ os | lower }}"
               changed_when: false
 
             - name: Create directories for repository files and RPM GPG keys