Add syntax highlighting to Advice for Humans window

[erikdarlingdata]

Summary

• Replaces plain monospace TextBox with color-coded styled text in the Advice for Humans window
• Blue section headers (=== ... ===)
• Red/orange/blue warning severity tags ([Critical], [Warning], [Info])
• Green CREATE INDEX statements with normalized indentation for multi-line blocks
• Grey labels with white values on key-value lines
• Red bold [SNIFFING] markers
• Clipboard copy still uses raw plain text

Test plan

• Open a plan with warnings, click Advice for Humans — text is color-coded
• Missing index CREATE statements are fully green including ON/INCLUDE lines
• ON/INCLUDE lines aligned with CREATE line
• Copy to Clipboard copies raw plain text (unchanged)
• Advice for Robots (JSON) still renders normally

🤖 Generated with Claude Code