re-scans become a monitor: -diff snapshots each target's normalized
findings to a per-target json file and, on the next run, surfaces only
the delta (+ new / - gone) against the last snapshot, then overwrites it
so each run diffs against the previous one. behavior is unchanged when
-diff is off.
new internal/store keys the set-difference off finding.Key (already
stable across runs) and uses only encoding/json + os - no new deps.
snapshot files are sanitized per target (no traversal), written 0600
under 0750 dirs. -store picks the location: explicit dir, else the log
dir, else <user-config>/sif/state. a missing snapshot is a clean
baseline, a corrupt one self-heals on the next save.
rolls the (c) 2022-2025 banner to 2022-2026 across all go files, the
startup banner in sif.go, and the header-check workflow's expected
format. comment-only, nothing else changes.
vmfunc