inc.sh: use BASH_SOURCE for path resolution; add --missingconfok; fix install.sh sourcing and git pull logic

setup_system.inc.sh: replace $(dirname "$0") with $(dirname "${BASH_SOURCE[0]:-$0}") so
paths resolve correctly whether the file is sourced or executed directly. Add --missingconfok
flag to warn-and-continue instead of prompting+aborting when config is missing. Fix machine_uuid
path (missing ../). Move `source config` into the else branch so it is not reached when
missingconfok skips the exit.

install.sh: source inc.sh instead of executing it as a subprocess so exported variables
(REPO_URL etc.) propagate back to the caller. Fix git-origin conflict handling: when reusing
an existing OEMDRV partition the user has already confirmed they want to keep it, so remove
the "fresh clone / wipe" option entirely. Now always pulls (fetch+checkout) when a git repo
is present; clears and fresh-clones only when no git repo exists on the partition.

basic_pre_script.inc: dot-source inc.sh so INSTALLDOCS and other config vars are available.

config.dist, sync_client_software.sh: rename UPGRADEURL/UPGRADEBRANCH to REPO_URL/REPO_BRANCH
to match the variable names already used in install.sh.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

install.md

@@ -52,7 +52,7 @@ Optionally add local per-machine overrides in `config.d/`:
 
 ```sh
 # Example: use the devel branch on this machine
-echo 'export UPGRADEBRANCH="devel"' > /opt/sys_config/config.d/system_defines.conf
+echo 'export REPO_BRANCH="devel"' > /opt/sys_config/config.d/system_defines.conf
 ```
 
 Once configured, boot the Fedora installer from USB — Anaconda will detect the `OEMDRV` partition and run the Kickstart automatically.