feat: add Chart, BarChart, Canvas components and enhance Viewport

[meszmate]

Changes

• Add Chart component with multi-dataset support, axes, grid, legends, and interpolation modes (linear, stepped, catmull-rom, monotone cubic)
• Add BarChart component with horizontal/vertical orientation and positive/negative baselines
• Add Canvas component for braille/block/dot/ascii plotting
• Enhance Sparkline with bucketing, gradients, summary modes, and configurable glyphs
• Enhance Viewport with word wrap, ANSI-aware horizontal scrolling, and customizable scrollbar chars/styles
• Add shared charting module for common types (Point, DataRange, Marker, etc.)
• Add Charts tab to showcase example
• Add standalone charts example with static snapshots and live sampled updates
• Add chart and viewport tests
• Update README with docs for all new components