style(ui): enhance console output with lipgloss styling

[EndersonPro]

Closes #19

Summary

• Add bordered card-style outputs for success, info, and dry-plan screens with adaptive light/dark terminal colors
• Replace ASCII table borders with Unicode box-drawing characters and add colored status indicators (green/muted/red dots)
• Style help and version commands with icons, visual hierarchy, and consistent formatting across all subcommands

Changes

File	Change
internal/ui/styles.go	Complete color palette, reusable card/box helpers, adaptive light/dark support
internal/ui/render.go	All render functions wrapped in styled cards with icons (📋 📁 ⚡ ✓)
internal/ui/table.go	Unicode box-drawing characters, colored headers, status-aware cell rendering
internal/ui/loading.go	Styled spinner frames with colored success/error messages
cmd/flutree/main.go	Styled help/version output with 🌳 icon, colored command names and descriptions
go.mod	Promote lipgloss from indirect to direct dependency

Test Plan

• All 137 tests pass across 11 packages
• Build succeeds without errors
• Manually tested help output (flutree --help, flutree create --help)
• Version output styled correctly (flutree --version → 🌳 flutree vdev)
• No business logic changes — only visual/output modifications
• Function signatures preserved — no breaking changes