fix: load mono font at all weights the CSS renders (avoid faux-bold)

[jowcy]

Problem

The typography guidance tells authors to pick a font pairing and load it via <link>, but never specifies which weights to request. The component patterns throughout the skill use the mono font at 400/500/600/700 (uppercase labels, table headers, status pills, the .opt cell) — yet several canonical examples ship a weight-limited mono:

• references/libraries.md loaded Space Mono at only 400;700.
• references/css-patterns.md's copy-paste "Theme Setup" block defaulted --font-mono to Space Mono (400/700 only), while the same file uses var(--font-mono) at font-weight: 600 (e.g. the code-file header label).

When a weight is used in CSS but absent from the <link>, the browser synthesizes it as faux-bold: smeared, lopsided glyphs — worst on monospace.

Real-world symptom: a generated page loaded Fira Code:wght@400;500 but used it at font-weight: 600/700, rendering mangled label text.

Changes

• SKILL.md — add a "load every weight you use — mono included" rule next to the pairing guidance, with the faux-bold warning.
• references/libraries.md
  • Make the canonical import example model the rule (symmetric full weights, swapping the weight-limited Space Mono illustration for IBM Plex Sans/Mono, which ship 400;500;600;700).
  • Add the same rule below the example.
  • Flag weight-limited monos (Fragment Mono = 400 only, Space Mono = 400/700) in the pairing table.
• references/css-patterns.md — switch the starter theme's default --font-mono from Space Mono to JetBrains Mono (full weight range), so the most-copied reference doesn't ship the faux-bold bug out of the box.

Notes

• Docs/guidance only — no template behavior changes. The bundled templates were already self-consistent (each loads every weight it uses, including mermaid-flowchart.html, which renders Fragment Mono only at 400).
• Space Mono and Fragment Mono remain valid listed pairings — they're just no longer defaults, and the new caveat steers them toward pages that stay within the weights they offer.
• Keeps the heavy-mono aesthetic intact by loading the weights the CSS renders, rather than weakening the CSS.