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>

tests/dark-mode-variable-contract.test.js

@@ -0,0 +1,23 @@
+// Westgate repaints Bootstrap's LIGHT colour mode dark, so every Bootstrap
+// variable that defaults to a near-black ink must be re-pointed at a light
+// token. Missing one is invisible until some component chains to it — that is
+// how /wiki/manage ended up with near-black table text on a near-black page.
+const assert = require("assert");
+const fs = require("fs");
+const path = require("path");
+
+const overrides = fs.readFileSync(
+	path.join(__dirname, "..", "scss", "overrides.scss"),
+	"utf8"
+);
+
+// Bootstrap's defaults for these are $black / $body-color-ish inks.
+["$body-color", "$body-bg", "$body-emphasis-color"].forEach(variable => {
+	const declaration = new RegExp(`\\${variable}:\\s*([^;]+);`).exec(overrides);
+	assert(declaration, `${variable} must be overridden for the dark repaint`);
+	assert.match(
+		declaration[1],
+		/\$wg-/,
+		`${variable} must resolve to a Westgate palette token, got: ${declaration[1].trim()}`
+	);
+});