Bash ${VAR} source: track literal assignments to avoid a wrong-directory false positive #2172

Follow-up to #2079 / #2139. That fix resolves source "${VAR}/lib/x.sh" by stripping the leading expansion and resolving the literal suffix against the script's own directory (the BENCH_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)" idiom). When the variable does NOT equal the script dir and a same-named decoy exists under the script dir, it binds to the wrong file.

Verified false positive: scripts/deploy.sh with ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)" sourcing "${ROOT}/lib/utils.sh" (real target <root>/lib/utils.sh) emits imports_from -> <root>/scripts/lib/utils.sh (the decoy under the script dir). It is bounded by the is_file() gate and flagged INFERRED, but it is a wrong edge to a real node.

Fix direction: track top-level literal assignments plus the dirname "${BASH_SOURCE[0]}" idiom (with optional /.. suffixes) for the leading variable and use that base; keep the script-dir guess only when the variable is untracked.