Add shellcheck fixes for selfmodel.sh warnings

[VictorVVedtion]

Description

selfmodel.sh has 4 shellcheck warnings (our CI runs with --severity=error so they don't fail the build, but they should be fixed):

• SC2034: SELFMODEL_REPO variable appears unused (line 8)
• SC2059: Variables in printf format string (line 370)
• SC2012: Use find instead of ls (line 628)
• SC2126: Use grep -c instead of grep | wc -l (line 783)

Files to modify

• scripts/selfmodel.sh

Acceptance criteria

• All 4 warnings resolved
• shellcheck --severity=style scripts/selfmodel.sh passes clean
• Script behavior unchanged