fix(tui): improve terminal compatibility and add minimum size guard

[bradymd]

Summary

• Broader ANSI regex: the previous pattern only matched CSI sequences; updated to also cover OSC, SS3, and other escape types that were leaking into rendered output
• Minimum terminal size guard: renders a friendly message instead of a broken layout when the terminal is smaller than 60×12
• Preview line normalization: strips \r and expands \t before truncating, preventing control characters from appearing in session previews
• Rune-aware truncation: replaces byte-indexed slicing with []rune slicing so multibyte (e.g. UTF-8 emoji/CJK) characters are never split mid-codepoint

Test plan

• Resize terminal below 60 wide or 12 tall — should see the "Terminal too small" message
• Resize back above threshold — layout should restore normally
• Open a session that emits OSC or other non-CSI escape sequences — confirm they don't appear as raw escape bytes in the preview
• Open a session whose output contains tabs or \r — confirm preview lines look clean

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