feat(tui): collapsible reasoning, randomized banner, tool label improvements

[buchenberg]

Summary

Collapsible Reasoning (TUI)

• Reasoning text (from models like DeepSeek) persists after streaming and collapses to a \▶ Reasoning...\ toggle
• Toggle appears chronologically before tool calls and assistant responses
• \ctrl+r\ toggles expand/collapse to review reasoning
• Cleared automatically on next user prompt

Tool Label Improvements

• \⏳ web_fetch → URL\ shows the URL being fetched
• Tool label renders above tool results instead of below
• Reasoning committed as standalone message before tool call starts (corrects chronological ordering)

Randomized Banner

• 20 curated figlet fonts picked randomly on each launch
• 20 taglines picked randomly
• Goat easter egg ASCII art gets lolcat rainbow coloring via new \�anner.Lolcat()\ helper

Files Changed

• \internal/tui/tui.go\ — Reasoning field on Message, collapse state, Flush/Done handlers, renderMessages ordering, \ctrl+r\ binding
• \internal/tui/tui_test.go\ — 12 new tests for reasoning lifecycle and rendering
• \internal/banner/banner.go\ — Random font/tagline, \Lolcat()\ helper, refactored \Generate()\
• \cmd/yaah/goat.go\ — Goat art now uses \�anner.Lolcat()\ for rainbow coloring