Fix health report rendering: tables, scrolling, emoji, wrapping

[jaredpar]

Health reports were rendering with several issues that made them hard to read in the terminal. This PR fixes all of them and adds a raw markdown toggle for debugging future rendering problems.

Problems fixed

• Raw markdown tables -- Tables rendered as pipe-delimited markdown text instead of formatted columns. Now rendered with aligned columns, dim separators, and proper word-wrapping within cells so no content is lost.
• No scrolling -- Health state and run detail pages used a single ReadKey without a scroll loop. Now supports Up/Down/PgUp/PgDn navigation.
• Garbled emoji -- Characters like the colored circles were mangled because console output encoding wasn't set. Added Console.OutputEncoding = Encoding.UTF8.
• Broken table layout from wrapping -- Tables wider than the terminal had their structure destroyed by the panel's line-wrapping logic. Now tables are width-constrained at render time: short columns (<=12 chars) keep their natural width, only wide columns shrink proportionally.
• "Malformed markup tag" crash -- WrapMarkupLine decoded escaped brackets ([[ to [) for width measurement but failed to re-escape them when rebuilding wrapped output. Spectre then treated literal [#83775] as a (malformed) tag. Fixed with EscapeBrackets() helper.

New feature

• [M]arkdown toggle -- Press M on health state or run detail pages to switch between rendered and raw markdown views. Useful for debugging rendering issues without leaving the dashboard.

Key design decisions

• Word-wrapping in table cells (not truncation) so all content remains visible
• Column width algorithm preserves short columns at natural width -- only columns wider than 12 chars get shrunk
• maxWidth parameter threaded from ContentWidth into ToMarkupLines and RenderTableAsText so tables are constrained before panel rendering, avoiding the wrapping layer that can't understand table structure

Testing

• 200 tests pass (added tests for emoji rendering, table word-wrapping, table constraining at multiple widths, and a comprehensive health report integration test that validates all rendered lines produce valid Spectre markup at various width/wrap combinations)