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>

README.md

@@ -166,6 +166,9 @@ Top-level host install/runtime settings. Use these keys under `system`.
 | `version`    | string     | empty                | Version selector for distro families     |
 | `filesystem` | string     | empty                | `btrfs`, `ext4`, or `xfs`                |
 | `name`       | string     | inventory hostname   | Final hostname                           |
+| `timezone`   | string     | `Europe/Vienna`      | System timezone (tz database name)       |
+| `locale`     | string     | `en_US.UTF-8`        | System locale                            |
+| `keymap`     | string     | `us`                 | Console keymap (`vconsole.conf`)         |
 | `id`         | int/string | empty                | VMID (required for Proxmox)              |
 | `cpus`       | int        | `0`                  | vCPU count                               |
 | `memory`     | int        | `0`                  | Memory in MiB                            |