bug: hardcoded developer git path at /home/user/sandbox/buskill-app/.git crashes upgrade flow

[RockyOmvi]

Describe the bug

src/packages/buskill/__init__.py lines 1995-2002 contain a hardcoded path to the developer's personal git sandbox:

result = subprocess.run( [
 'git',
 '--git-dir=/home/user/sandbox/buskill-app/.git',
 ...
] )

When BUSKILL_VERSION['SOURCE_DATE_EPOCH'] is empty (which happens in development/testing builds), the code tries to run git against a repository at /home/user/sandbox/buskill-app/.git. On any system other than the original developer's machine, this path does not exist, causing the command to fail with fatal: not a git repository.

Steps to reproduce

1. Build or run BusKill in an environment where SOURCE_DATE_EPOCH is not set
2. Trigger the upgrade check path
3. The upgrade flow crashes with an unhandled exception or hangs

Expected behavior

The git path should be determined dynamically using a configurable setting or by searching for a .git directory relative to the project root, not hardcoded to a developer-specific path.

Code reference

src/packages/buskill/__init__.py:1995-2002:

if BUSKILL_VERSION['SOURCE_DATE_EPOCH'] == '':
    result = subprocess.run( [
     'git',
     '--git-dir=/home/user/sandbox/buskill-app/.git',
     ...
    ] )