fix: light emphasis colour so plain Bootstrap tables are readable (#36)

/wiki/manage rendered its table in near-black on the near-black page.
The theme repaints Bootstrap's LIGHT colour mode dark but never overrode
$body-emphasis-color, which Bootstrap defaults to $black. Any component
that chains to --bs-emphasis-color inherited that ink: plain .table text
and header cells, tooltips (dark text on dark background), nav-tabs and
nav-underline active links, and list-group hover states.

Point it at $wg-text, next to the other body colour overrides, instead of
patching .table per page. Verified in the sow-nodebb dev stack against a
seeded wiki namespace: the manage table, topics, categories, notifications
and account pages all render correctly.

Also refresh AGENTS.md "How To Test" for the current `make dev*` loop and
state that a theme change can always be checked on a live local forum.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

scss/overrides.scss

@@ -48,6 +48,12 @@ $dark:          $wg-ink !default;
 
 $body-color: $wg-text-soft !default;
 $body-bg: $wg-ink !default;
+// We repaint Bootstrap's LIGHT colour mode dark, so emphasis must be light too.
+// Bootstrap defaults it to $black; leaving it there paints near-black text on our
+// dark surfaces wherever a component chains to --bs-emphasis-color: plain .table
+// (e.g. /wiki/manage), tooltips, nav-tabs/nav-underline active links, list-group
+// hover states, and the .text-emphasis / .link-body-emphasis utilities.
+$body-emphasis-color: $wg-text !default;
 $body-tertiary-bg: $wg-panel !default;
 $text-muted: $wg-text-muted !default;
 $border-color: rgba($wg-gold, 0.14) !default;