fix(viewer): make glossary term links actually visible on item pages (#1430)

fix(viewer): make glossary term links actually visible on item pages (#1430)

.gloss-term relied on color: var(--link) + a 1px dotted border-bottom for
affordance. Neither worked in practice: --link resolves to the exact same
value as --text (#222) site-wide, and a 1px border-bottom rendered as a
barely-visible sub-pixel line at this font size/DPI. The link was fully
functional (click -> modal) but visually indistinguishable from plain text.

Switches to text-decoration (scales correctly with font size, unlike
border-bottom) plus var(--heading)/var(--gold-dark) - colors already used
elsewhere in the theme as visible accents, unlike --link.

Verified in-browser against the real published data: computed color is now
a distinct brown/gold (#4C420E) with a visible dotted underline, and the
click-to-modal behavior is unaffected.
EOF

Co-authored-by: Pascal HAVELANGE <havelangep@hotmail.com>