Initial commit: terminal file browser & markdown viewer

A beautiful TUI for browsing files and reading markdown/code:
- Two-pane layout with file tree and content viewer
- Markdown rendering via Glamour
- Syntax highlighting via Chroma
- Auto-detects light/dark terminal theme
- Arrow key navigation, Esc to go back
- Page Up/Down, Home/End for scrolling

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

theme.go

@@ -0,0 +1,196 @@
+package main
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/charmbracelet/lipgloss"
+	"github.com/muesli/termenv"
+)
+
+// Theme represents a color theme
+type Theme struct {
+	Name string
+
+	// UI colors
+	Base     lipgloss.Color
+	Surface  lipgloss.Color
+	Overlay  lipgloss.Color
+	Text     lipgloss.Color
+	Subtext  lipgloss.Color
+	Accent   lipgloss.Color
+	Blue     lipgloss.Color
+	Teal     lipgloss.Color
+	Green    lipgloss.Color
+	Yellow   lipgloss.Color
+	Orange   lipgloss.Color
+	Red      lipgloss.Color
+	Purple   lipgloss.Color
+
+	// For code highlighting
+	ChromaStyle   string
+	GlamourStyle  string
+	LineNumColor  string
+}
+
+var (
+	// LightTheme for light terminal backgrounds
+	LightTheme = Theme{
+		Name:     "light",
+		Base:     lipgloss.Color("#f5f5f5"),
+		Surface:  lipgloss.Color("#e8e8e8"),
+		Overlay:  lipgloss.Color("#c0c0c0"),
+		Text:     lipgloss.Color("#1a1a1a"),
+		Subtext:  lipgloss.Color("#505050"),
+		Accent:   lipgloss.Color("#6366f1"),
+		Blue:     lipgloss.Color("#2563eb"),
+		Teal:     lipgloss.Color("#0d9488"),
+		Green:    lipgloss.Color("#16a34a"),
+		Yellow:   lipgloss.Color("#ca8a04"),
+		Orange:   lipgloss.Color("#ea580c"),
+		Red:      lipgloss.Color("#dc2626"),
+		Purple:   lipgloss.Color("#9333ea"),
+
+		ChromaStyle:  "github",
+		GlamourStyle: "light",
+		LineNumColor: "#888888",
+	}
+
+	// DarkTheme for dark terminal backgrounds
+	DarkTheme = Theme{
+		Name:     "dark",
+		Base:     lipgloss.Color("#1e1e2e"),
+		Surface:  lipgloss.Color("#313244"),
+		Overlay:  lipgloss.Color("#45475a"),
+		Text:     lipgloss.Color("#cdd6f4"),
+		Subtext:  lipgloss.Color("#a6adc8"),
+		Accent:   lipgloss.Color("#b4befe"),
+		Blue:     lipgloss.Color("#89b4fa"),
+		Teal:     lipgloss.Color("#94e2d5"),
+		Green:    lipgloss.Color("#a6e3a1"),
+		Yellow:   lipgloss.Color("#f9e2af"),
+		Orange:   lipgloss.Color("#fab387"),
+		Red:      lipgloss.Color("#f38ba8"),
+		Purple:   lipgloss.Color("#cba6f7"),
+
+		ChromaStyle:  "catppuccin-mocha",
+		GlamourStyle: "dark",
+		LineNumColor: "#6c7086",
+	}
+
+	// CurrentTheme is the active theme
+	CurrentTheme = LightTheme
+)
+
+// DetectTheme tries to detect if terminal has dark or light background
+func DetectTheme() Theme {
+	// Check for config file override first
+	if theme := loadThemePreference(); theme != "" {
+		if theme == "dark" {
+			return DarkTheme
+		}
+		return LightTheme
+	}
+
+	// Auto-detect from terminal
+	if termenv.NewOutput(os.Stdout).HasDarkBackground() {
+		return DarkTheme
+	}
+	return LightTheme
+}
+
+// SetTheme sets the current theme and updates all styles
+func SetTheme(t Theme) {
+	CurrentTheme = t
+	updateStyles()
+}
+
+// loadThemePreference loads theme from config file
+func loadThemePreference() string {
+	configDir, err := os.UserConfigDir()
+	if err != nil {
+		return ""
+	}
+
+	configPath := filepath.Join(configDir, "reader", "theme")
+	data, err := os.ReadFile(configPath)
+	if err != nil {
+		return ""
+	}
+
+	return strings.TrimSpace(string(data))
+}
+
+// SaveThemePreference saves theme preference to config file
+func SaveThemePreference(theme string) error {
+	configDir, err := os.UserConfigDir()
+	if err != nil {
+		return err
+	}
+
+	readerDir := filepath.Join(configDir, "reader")
+	if err := os.MkdirAll(readerDir, 0755); err != nil {
+		return err
+	}
+
+	configPath := filepath.Join(readerDir, "theme")
+	return os.WriteFile(configPath, []byte(theme), 0644)
+}
+
+// updateStyles updates all the lipgloss styles based on current theme
+func updateStyles() {
+	t := CurrentTheme
+
+	activeBorderStyle = lipgloss.NewStyle().
+		Border(lipgloss.RoundedBorder()).
+		BorderForeground(t.Accent)
+
+	inactiveBorderStyle = lipgloss.NewStyle().
+		Border(lipgloss.RoundedBorder()).
+		BorderForeground(t.Overlay)
+
+	directoryStyle = lipgloss.NewStyle().
+		Foreground(t.Blue).
+		Bold(true)
+
+	fileStyle = lipgloss.NewStyle().
+		Foreground(t.Text)
+
+	selectedStyle = lipgloss.NewStyle().
+		Background(t.Surface).
+		Foreground(t.Accent).
+		Bold(true)
+
+	statusBarStyle = lipgloss.NewStyle().
+		Background(t.Surface).
+		Foreground(t.Subtext).
+		Padding(0, 1)
+
+	statusKeyStyle = lipgloss.NewStyle().
+		Background(t.Overlay).
+		Foreground(t.Text).
+		Padding(0, 1)
+
+	helpStyle = lipgloss.NewStyle().
+		Border(lipgloss.RoundedBorder()).
+		BorderForeground(t.Purple).
+		Padding(1, 2)
+
+	helpTitleStyle = lipgloss.NewStyle().
+		Foreground(t.Purple).
+		Bold(true).
+		MarginBottom(1)
+
+	helpKeyStyle = lipgloss.NewStyle().
+		Foreground(t.Yellow).
+		Width(12)
+
+	helpDescStyle = lipgloss.NewStyle().
+		Foreground(t.Subtext)
+
+	titleStyle = lipgloss.NewStyle().
+		Foreground(t.Accent).
+		Bold(true).
+		Padding(0, 1)
+}