feat(benchmarks): expand multilingual stemming quality evaluation

* cover all Radixor dictionary languages
* add PRIMARY_OUTPUT, ANY_CANDIDATE, and ALL_CANDIDATES policies
* measure pairwise over-stemming and under-stemming
* add balanced accuracy and complementary quality metrics
* compare single-output and multi-output stemmers fairly
* improve result validation, reporting, and documentation
* move stemming quality tests into the standard test source set
* preserve the existing JMH benchmark structure and badge output

docs/assets/stylesheets/extra.css

@@ -67,6 +67,104 @@
   padding: 0.45rem 0.7rem;
 }
 
+/* Publication-quality benchmark tables retain identity columns while scrolling. */
+.quality-table {
+  max-width: 100%;
+  overflow-x: auto;
+  margin: 0.65rem 0 1rem;
+  border: 1px solid var(--md-default-fg-color--lightest);
+  border-radius: 0.2rem;
+  scrollbar-gutter: stable;
+}
+
+.quality-table:focus {
+  outline: 0.15rem solid var(--md-accent-fg-color);
+  outline-offset: 0.1rem;
+}
+
+.quality-table::before {
+  content: "Scrollable table: Rank, Stemmer, and Output policy remain visible.";
+  display: block;
+  padding: 0.35rem 0.55rem;
+  color: var(--md-default-fg-color--light);
+  font-size: 0.68rem;
+}
+
+.quality-table .md-typeset__table,
+.quality-table table {
+  margin: 0;
+}
+
+.quality-table table th:nth-child(1),
+.quality-table table td:nth-child(1),
+.quality-table table th:nth-child(2),
+.quality-table table td:nth-child(2),
+.quality-table table th:nth-child(3),
+.quality-table table td:nth-child(3) {
+  position: sticky;
+  z-index: 2;
+  background: var(--md-default-bg-color);
+  background-clip: padding-box;
+}
+
+.quality-table table th:nth-child(1),
+.quality-table table td:nth-child(1) {
+  left: 0;
+  min-width: 2.8rem;
+}
+
+.quality-table table th:nth-child(2),
+.quality-table table td:nth-child(2) {
+  left: 2.8rem;
+  min-width: 13rem;
+  white-space: normal;
+}
+
+.quality-table table th:nth-child(3),
+.quality-table table td:nth-child(3) {
+  left: 15.8rem;
+  min-width: 8.5rem;
+  box-shadow: 0.2rem 0 0.25rem rgb(0 0 0 / 8%);
+}
+
+.quality-details > summary {
+  font-weight: 600;
+}
+
+@media screen and (max-width: 44.99em) {
+  .quality-table table th:nth-child(2),
+  .quality-table table td:nth-child(2) {
+    min-width: 10rem;
+  }
+
+  .quality-table table th:nth-child(3),
+  .quality-table table td:nth-child(3) {
+    position: static;
+    min-width: 7.5rem;
+    box-shadow: none;
+  }
+}
+
+@media print {
+  .quality-table {
+    overflow: visible;
+    border: 0;
+  }
+
+  .quality-table::before {
+    display: none;
+  }
+
+  .quality-table table th,
+  .quality-table table td {
+    position: static !important;
+  }
+
+  .quality-details:not([open]) > *:not(summary) {
+    display: block;
+  }
+}
+
 /* Code blocks */
 .md-typeset pre > code {
   font-size: 0.72rem;