v0.5.9 — TUI redesign + animate-core value tweens

TUI Redesign

Six major improvements to the TUI:

1. Single-letter slash commands removed — /c /m /t /s /h /q /e /d /? /ss deleted; long forms only
2. Token/ctx widget fix — stream_options.include_usage for providers that omit streamed usage by default
3. Auto-scroll pinned to bottom — usize::MAX sentinel replaces message-index math
4. Permission popup redesign — rounded border, themed title, padded content, Y/N/A badges
5. Tool-call transparency — framed cards, 6-line collapsed / 40-line expanded, footer hints
6. Aesthetic redesign — rounded borders, branded ◆ pawan title, badge-pill role headers, muted timestamps

Motion & value animation

• animate-core value tweens — rolling token counts (600ms cubic-out), eased ctx% bar (450ms cubic-out), accent-colour fade on /theme switches
• tachyonfx cell effects — content reveal, popup sweep-in, status pulse
• tui-scrollview adoption — automatic vertical scrollbar
• ratatui-cheese spinner — animated "Pawan is thinking..."
• Rect::centered() — all overlay modals use centered constraints

Refactoring

• Removed ColorTransition struct + ease_out_cubic/lerp_u8/extract_rgb helpers
• Removed dead tui/scrollbar.rs module
• Removed unused one_line_preview + 7 tests
• Extracted tui/effects.rs for unified motion + value animation

Dependencies

• animate-core = "0.4.1" (gated behind tui feature) — skipped broken animate facade

Verification

• ✅ cargo build --workspace — clean
• ✅ cargo clippy --all-targets — clean
• ✅ 1750 tests pass (0 failures, 12 ignored)

See CHANGELOG.md for full details.