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).

decnet_web/src/components/Dashboard.css

@@ -2,6 +2,7 @@
   display: flex;
   flex-direction: column;
   gap: 24px;
+  min-height: 100%;
 }
 
 /* Page header */
@@ -219,6 +220,7 @@
   border: 1px solid var(--border-color);
   display: flex;
   flex-direction: column;
+  min-height: 0;
 }
 
 .section-header {
@@ -258,12 +260,24 @@
   display: grid;
   grid-template-columns: 2fr 1fr;
   gap: 16px;
+  flex: 1;
+  min-height: 0;
+}
+
+.dash-grid > .logs-section .logs-table-container {
+  flex: 1;
+  max-height: none;
 }
 
 .dash-side {
   display: flex;
   flex-direction: column;
   gap: 16px;
+  min-height: 0;
+}
+
+.dash-side > .logs-section {
+  flex: 1;
 }
 
 /* Attacker/siege rows */
@@ -363,6 +377,7 @@
   overflow-x: auto;
   overflow-y: auto;
   max-height: 420px;
+  min-height: 0;
 }
 
 .logs-table {

decnet_web/src/components/Layout.css

@@ -56,10 +56,16 @@
 }
 
 .sidebar-nav {
-  flex-grow: 1;
+  flex: 1 1 0;
+  min-height: 0;
+  overflow-y: auto;
   padding: 20px 0;
 }
 
+.sidebar-footer {
+  flex-shrink: 0;
+}
+
 .nav-item {
   display: flex;
   align-items: center;