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/lexers/lexers.go

@@ -29,6 +29,12 @@ func Names(withAliases bool) []string {
 	return GlobalLexerRegistry.Names(withAliases)
 }
 
+// Aliases of all the lexers, and skip those lexers who do not have any aliases,
+// or show their name instead
+func Aliases(skipWithoutAliases bool) []string {
+	return GlobalLexerRegistry.Aliases(skipWithoutAliases)
+}
+
 // Get a Lexer by name, alias or file extension.
 //
 // Note that this if there isn't an exact match on name or alias, this will