Project refactor, add anthropic API support

- Split pkg/cli/cmd.go into new pkg/cmd package
- Split pkg/cli/functions.go into pkg/lmcli/tools package
- Refactor pkg/cli/openai.go to pkg/lmcli/provider/openai

Other changes:

- Made models configurable
- Slight config reorganization

pkg/util/tty/highlight.go

@@ -0,0 +1,60 @@
+package tty
+
+import (
+	"io"
+	"strings"
+
+	"github.com/alecthomas/chroma/v2"
+	"github.com/alecthomas/chroma/v2/formatters"
+	"github.com/alecthomas/chroma/v2/lexers"
+	"github.com/alecthomas/chroma/v2/styles"
+)
+
+type ChromaHighlighter struct {
+	lexer     chroma.Lexer
+	formatter chroma.Formatter
+	style     *chroma.Style
+}
+
+func NewChromaHighlighter(lang, format, style string) *ChromaHighlighter {
+	l := lexers.Get(lang)
+	if l == nil {
+		l = lexers.Fallback
+	}
+	l = chroma.Coalesce(l)
+
+	f := formatters.Get(format)
+	if f == nil {
+		f = formatters.Fallback
+	}
+
+	s := styles.Get(style)
+	if s == nil {
+		s = styles.Fallback
+	}
+
+	return &ChromaHighlighter{
+		lexer:     l,
+		formatter: f,
+		style:     s,
+	}
+}
+
+func (s *ChromaHighlighter) Highlight(w io.Writer, text string) error {
+	it, err := s.lexer.Tokenise(nil, text)
+	if err != nil {
+		return err
+	}
+	return s.formatter.Format(w, s.style, it)
+}
+
+func (s *ChromaHighlighter) HighlightS(text string) (string, error) {
+	it, err := s.lexer.Tokenise(nil, text)
+	if err != nil {
+		return "", err
+	}
+	sb := strings.Builder{}
+	sb.Grow(len(text) * 2)
+	s.formatter.Format(&sb, s.style, it)
+	return sb.String(), nil
+}