feat: add terminal chart visualization for financial data

[liuxiaopai-ai]

Closes #63

Adds automatic Unicode chart rendering for financial data in agent responses. Charts are appended below existing tables — the original table output is preserved.

What it does

When the agent returns a markdown table with numeric data, the formatter now detects chart opportunities and appends a visual:

Bar chart — for comparison data (e.g. company revenue side-by-side):

  📊 Revenue
  
  Apple             ██████████████████████████████████████  $394.3B
  Google            ████████████████████████████████        $307.4B
  Microsoft         ████████████████████████████            $245.1B

Sparkline — for time-series trends (e.g. quarterly earnings):

  📈 Revenue (2020–2024)
  ▁▂▅▇█  $274.5B → $394.3B (+43.6%)

How it works

• detectChartOpportunity() analyzes parsed table columns — if it finds a label/date column paired with a numeric column, it suggests a chart type
• Date-like labels (years, quarters, YYYY-MM) → sparkline; otherwise → bar chart
• Integrated into the existing formatResponse() pipeline, runs before table boxing
• Uses theme colors (colors.primary) and respects dimensions.boxWidth

Changes

File	What
src/utils/charts.ts	Chart engine — bar chart, sparkline, detection, number formatting
src/utils/charts.test.ts	32 tests covering all chart functions and edge cases
src/utils/markdown-table.ts	2-line integration into formatResponse()

Tests

32 new tests, all passing. Full suite (41 tests) green. bun run typecheck clean.