fix(backend): keep fig-/feat- tags by slug, not just name

The live store marks the figure/feature tag families on the tag SLUG
(slug 'fig-chat', display name 'Chatoyant'), but _scoped_tags filtered on
name.startswith('fig-'), so all 11 fig-* tags were silently dropped at sync
and the figure-tag echo (METADATA-30) had nothing to draw from. Match the
prefix on slug OR name. Adds a test for the slug-prefixed bare-name shape.

backend/taxonomy.py

@@ -19,7 +19,14 @@ def _now_iso() -> str:
 
 
 def _scoped_tags(tags: list[dict]) -> list[dict]:
-    return [t for t in tags if t.get("name", "").startswith(("fig-", "feat-"))]
+    # The fig-/feat- family marker is on the tag SLUG (e.g. slug 'fig-chat',
+    # name 'Chatoyant'), not the display name. Match either so a store that
+    # prefixes the name instead of the slug is also kept.
+    return [
+        t for t in tags
+        if (t.get("slug", "").startswith(("fig-", "feat-"))
+            or t.get("name", "").startswith(("fig-", "feat-")))
+    ]
 
 
 def _normalize_category(c: dict) -> tuple: