fix(content): keep desktop markers and align narrow-screen headings

[hakula139]

Summary

• Keep article heading text aligned with body text. Below 1280px, the heading is a section link that turns blue on hover or keyboard focus. At desktop widths, it keeps its normal color and reveals the original # marker on hover or focus.
• Use one native section link with a desktop-only CSS marker. Remove heading link underlines, preserve the h2 divider, and wrap long headings. Preserve inline formatting and existing authored links, and leave callout and blockquote headings unchanged.
• Retain merged floating controls from fix(layout): group floating controls and clear the footer #85 and native callouts from fix(content): use native details for stable callouts #86.

Verification

• pnpm build, pnpm format, pnpm lint, pnpm spellcheck, nix flake check, commit hooks, git diff --check, and CSS sync passed for the theme. The consuming site passed the same checks and its minified build rendered and indexed 75 pages after CSS generation.
• Managed headless Chromium checked the generated LR2 / BMS and FFT articles at 320px, 390px, 768px, 1279px, 1280px, and 1440px in light and dark themes. Heading text aligned with body text, section links stayed inside the cards, and pages had no horizontal overflow. Default typography, responsive hover / focus colors, no link underlines, desktop marker visibility and containment, focus outlines, and Enter fragment navigation passed.
• Long Chinese and unbroken Latin heading probes wrapped within the card. Inline emphasis and code were preserved, authored links remained intact without nested anchors, and repeated initialization did not duplicate heading links.
• Browser checks used generated assets with external resources excluded. Local Nix validation covered aarch64-darwin. Other browser engines and Nix systems were not tested locally.