feat: Phase 2 UX Polish — theme system, config profiles, error banner, tests

- Add Theme struct with 3 predefined themes (dark/light/druntime)
- Add Profile struct for named configuration profiles
- Add ErrorBanner with severity levels and auto-dismiss
- Add unit tests for theme, error banner, and models
- Update CHANGELOG.md and PROJECT_STATE.md

pkg/tui/error_banner.go

@@ -0,0 +1,137 @@
+package tui
+
+import (
+	"fmt"
+	"strings"
+	"time"
+
+	"github.com/charmbracelet/lipgloss"
+)
+
+// ErrorSeverity indicates the level of an error message
+type ErrorSeverity int
+
+const (
+	SevError ErrorSeverity = iota
+	SevWarning
+	SevInfo
+)
+
+// ErrorBanner displays a structured error message with title, details, and hints
+type ErrorBanner struct {
+	Title       string
+	Detail      string
+	Hints       []string
+	Severity    ErrorSeverity
+	AutoDismiss bool
+	DismissAfter time.Duration
+	createdAt   time.Time
+	visible     bool
+}
+
+// NewErrorBanner creates a new error banner with the given severity
+func NewErrorBanner(severity ErrorSeverity) *ErrorBanner {
+	return &ErrorBanner{
+		Severity:     severity,
+		AutoDismiss:  true,
+		DismissAfter: 5 * time.Second,
+		visible:      false,
+	}
+}
+
+// Show displays the error banner with the given message
+func (b *ErrorBanner) Show(title, detail string, hints ...string) {
+	b.Title = title
+	b.Detail = detail
+	b.Hints = hints
+	b.visible = true
+	b.createdAt = time.Now()
+}
+
+// Hide hides the error banner
+func (b *ErrorBanner) Hide() {
+	b.visible = false
+}
+
+// IsVisible returns whether the banner is currently visible
+func (b *ErrorBanner) IsVisible() bool {
+	return b.visible
+}
+
+// Update checks if auto-dismiss time has elapsed
+func (b *ErrorBanner) Update() {
+	if b.visible && b.AutoDismiss && time.Since(b.createdAt) > b.DismissAfter {
+		b.visible = false
+	}
+}
+
+// View renders the error banner
+func (b *ErrorBanner) View(width int) string {
+	if !b.visible {
+		return ""
+	}
+
+	var (
+		titleStyle lipgloss.Style
+		borderColor lipgloss.Color
+		prefix     string
+	)
+
+	switch b.Severity {
+	case SevError:
+		titleStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("#ea6962")).Bold(true)
+		borderColor = lipgloss.Color("#ea6962")
+		prefix = "✖"
+	case SevWarning:
+		titleStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("#d8a657")).Bold(true)
+		borderColor = lipgloss.Color("#d8a657")
+		prefix = "⚠"
+	case SevInfo:
+		titleStyle = lipgloss.NewStyle().Foreground(lipgloss.Color("#7daea3")).Bold(true)
+		borderColor = lipgloss.Color("#7daea3")
+		prefix = "ℹ"
+	}
+
+	var sb strings.Builder
+
+	// Title line with prefix
+	sb.WriteString(titleStyle.Render(fmt.Sprintf("%s %s", prefix, b.Title)))
+
+	// Detail line
+	if b.Detail != "" {
+		sb.WriteString("\n")
+		sb.WriteString(strings.Repeat(" ", len(prefix)+1))
+		detailStyle := lipgloss.NewStyle().Foreground(activeTheme.Fg)
+		sb.WriteString(detailStyle.Render(b.Detail))
+	}
+
+	// Hints
+	if len(b.Hints) > 0 {
+		sb.WriteString("\n")
+		sb.WriteString(strings.Repeat(" ", len(prefix)+1))
+		hintStyle := lipgloss.NewStyle().Foreground(activeTheme.FgMute)
+		sb.WriteString(hintStyle.Render("Hints:"))
+		for i, hint := range b.Hints {
+			sb.WriteString("\n")
+			sb.WriteString(strings.Repeat(" ", len(prefix)+2))
+			sb.WriteString(hintStyle.Render(fmt.Sprintf("%d. %s", i+1, hint)))
+		}
+	}
+
+	// Wrap in a styled box
+	borderStyle := lipgloss.NewStyle().
+		Border(lipgloss.RoundedBorder()).
+		BorderForeground(borderColor).
+		Padding(0, 1).
+		Width(min(width-2, 80))
+
+	return borderStyle.Render(sb.String())
+}
+
+// min returns the smaller of two integers
+func min(a, b int) int {
+	if a < b {
+		return a
+	}
+	return b
+}