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/alecthomas/chroma/v2/registry.go

@@ -48,6 +48,24 @@ func (l *LexerRegistry) Names(withAliases bool) []string {
 	return out
 }
 
+// Aliases of all the lexers, and skip those lexers who do not have any aliases,
+// or show their name instead
+func (l *LexerRegistry) Aliases(skipWithoutAliases bool) []string {
+	out := []string{}
+	for _, lexer := range l.Lexers {
+		config := lexer.Config()
+		if len(config.Aliases) == 0 {
+			if skipWithoutAliases {
+				continue
+			}
+			out = append(out, config.Name)
+		}
+		out = append(out, config.Aliases...)
+	}
+	sort.Strings(out)
+	return out
+}
+
 // Get a Lexer by name, alias or file extension.
 func (l *LexerRegistry) Get(name string) Lexer {
 	if lexer := l.byName[name]; lexer != nil {