style(log-viewer): one type scale and one mono family

[lukecotter]

What

One type scale and one mono family for the whole webview, replacing hand-written pixel sizes and bare monospace literals.

Why

Text sizes were set per component, so the same kind of text read at a different size depending on where it sat, and none of it followed the reader's VS Code font size. Code-shaped text picked its family per file.

How

• Type scale on VS Code's own ramp, in styles/tokens.css:
  • --lana-text-lg → --vscode-bodyFontSize (13px)
  • --lana-text-base → --vscode-bodyFontSize-small (12px)
  • --lana-text-sm → --vscode-bodyFontSize-xSmall (11px)
  • --lana-text-xs → 0.84 × base (10px)
  • --lana-text-caps + --lana-text-caps-tracking for section headers
• One mono token — --lana-font-mono → var(--vscode-editor-font-family, monospace) — carries the only non-VS-Code-host fallback. Applied to the table name columns, group rows, tooltips and code blocks.
• All-caps runs step one size down: caps reach cap height on every glyph, so at the same nominal size they read larger than the mixed-case text beside them.
• Canvas text is untouched — a PIXI font string cannot read a CSS variable.

Notes

• No behaviour change; sizes and families only.
• The grid still sets its cell size from --vscode-editor-font-size, so a large editor font puts grid cells a step above the app base. Left as is — a separate decision.

Testing

• tsc -b --force, eslint, jest (1552 tests / 121 suites) and the production build all pass.
• Checked in a dark and a light theme, and with the editor font size changed.