chore: dashboard layout polish + sqlite_vec dependency

* Dashboard / Layout / index CSS — flexbox cleanup so the sidebar
  scrolls independently and dashboard panels fill available height
  without overflowing the viewport (min-height: 0 on the flex
  ancestors that were collapsing).
* pyproject.toml — add sqlite_vec runtime dep (groundwork for an
  embeddings-backed feature ANTI is wiring up separately).

pyproject.toml

@@ -38,7 +38,8 @@ dependencies = [
     "python-multipart>=0.0.20",
     "httpx>=0.28.1",
     "requests>=2.33.1",
-    "slowapi>=0.1.9"
+    "slowapi>=0.1.9",
+    "sqlite_vec>=0.1.9"
 ]
 
 [project.optional-dependencies]