chore: modernize CI and update Go toolchain

- Bump Go from 1.19 to 1.26 and update all dependencies
- Rewrite CI workflow with matrix strategy (Linux, macOS, Windows)
- Update GitHub Actions to current versions (checkout@v4, setup-go@v5)
- Update CodeQL actions from v1 to v3
- Fix cross-platform bug in mock/path.go (path.Join -> filepath.Join)
- Clean up dependabot config (weekly schedule, remove stale ignore)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vendor/github.com/dlclark/regexp2/syntax/parser.go

@@ -553,10 +553,10 @@ func (p *parser) scanRegex() (*regexNode, error) {
 			}
 
 		case '.':
-			if p.useOptionE() {
-				p.addUnitSet(ECMAAnyClass())
-			} else if p.useOptionS() {
+			if p.useOptionS() {
 				p.addUnitSet(AnyClass())
+			} else if p.useOptionE() {
+				p.addUnitSet(ECMAAnyClass())
 			} else {
 				p.addUnitNotone('\n')
 			}