checkDatabaseErrors matched db error regexes against each response with
no baseline, so a site serving a shared error template, custom 500 or
waf block page containing a db error string reported an identical
high-severity sql injection finding on every probed path. capture the
main-url response as a baseline and skip, per pattern, any error string
already present in it while still checking other patterns, so only
differential probe-caused errors are reported.
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.
