fix(glossy): fix forward linking (broken themes)

Fixes [#19](https://github.com/swaits/typst-collection/issues/19).

Themes must emit `entry.label` for terms to be able to forward-link to
their glossary entrie.

glossy/tests/forward-links/test.typ

@@ -0,0 +1,45 @@
+#import "/lib.typ": *
+#import "@preview/glossarium:0.5.1": *
+
+#set page(height: auto, width: 4.5in)
+#show link: set text(fill: red)
+
+// -----------------------------------------------------------------------------
+
+= `glossy`:
+
+#box(
+  stroke: 1pt,
+  inset: 1em,
+  [
+    #show: init-glossary.with((WWW: "World Wide Web"))
+
+    This should be a link: @WWW
+
+    This should be a link, too: @WWW
+
+    #glossary()
+  ]
+)
+
+// -----------------------------------------------------------------------------
+
+= `glossarium`:
+
+#box(
+  stroke: 1pt,
+  inset: 1em,
+  [
+    #show: make-glossary
+    #let entry-list = (
+      (key: "ML", short: "ML", long: "Machine Learning"),
+    )
+    #register-glossary(entry-list)
+
+    This should be a link: @ML
+
+    This should be a link, too: @ML
+
+    #print-glossary(entry-list)
+  ]
+)