feat(web): pin Logging/History/Network as a resizable column (#1616)

Add the ability to "pin" the Logging, History, and Network screens into a
second column on the right of the InspectorView, so a primary screen and a
monitor screen are visible at once (e.g. watch Logs while calling a Tool).

- A "pin as column" button on the Logs/History/Network panel toolbars opens
  the column (shown only when wide + connected).
- The column hosts a MonitoringControls tab row (available monitor tabs +
  close) over the selected embedded screen. Pinning removes the monitor group
  from the header tab bar; closing (x) returns it.
- The divider between the primary area and the column is draggable (pointer +
  keyboard); width is clamped and persisted.
- The split collapses to one column below ~1040px (the ServerListScreen
  single-card breakpoint) and while disconnected, without discarding the pin
  preference — it reopens when wide + connected again.

State (pinned/tab/width) is view-local and persisted via the existing
useLocalStorage pattern, so no new props thread through App and ViewHeader is
unchanged (it just receives a filtered tab list). Screens/panels gain an
`embedded` mode (fills the parent height, drops the 340px filter sidebar) via a
shared EmbeddableScrollArea element.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

clients/web/src/App.css

@@ -422,3 +422,30 @@
   z-index: 200;
   box-shadow: var(--mantine-shadow-sm);
 }
+
+/*
+ * Draggable vertical divider between the primary screen area and the pinned
+ * monitoring column (#1616). The col-resize cursor, the hover/active accent,
+ * and the drag-time user-select suppression are all pseudo-selector / cursor /
+ * cross-element concerns that can't be expressed as Mantine props, so the whole
+ * unit lives here rather than split across the theme.
+ */
+.resize-handle {
+  flex: 0 0 auto;
+  width: 6px;
+  cursor: col-resize;
+  background-color: var(--inspector-border-default);
+  transition: background-color 120ms ease;
+  touch-action: none;
+}
+
+.resize-handle:hover,
+.resize-handle:focus-visible {
+  background-color: var(--mantine-primary-color-filled);
+}
+
+/* Suppress text selection anywhere on the page while a drag is in progress. */
+body.resizing-col {
+  user-select: none;
+  cursor: col-resize;
+}