Home mosaic, multi-select delete, offline banner and loading states

- Home puts the dashboards beside the flows: two equal-height columns,
  capped and scrollable, most recently worked on first. Each tile is a
  schematic footprint built from the stored widget placements.
- Flows and dashboards can be picked by long press or ctrl-click; the
  create button becomes a trash and one dialog covers the batch.
- The offline banner is drawn on the body so it centres on the viewport,
  and the live socket now releases the offline latch a stray 503 set.
- A boot spinner before React's first commit, a router pending screen for
  code-split pages, and skeletons where an empty list used to flash.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018tULRZJUkZsw7rMJ3h4xvu

frontend/src/components/Flow/useFlowSocket.ts

@@ -144,7 +144,7 @@ function connect() {
     retry = RECONNECT_MIN
     rejected = 0
     liveStore.setConnected(true)
-    connectionStore.setOnline()
+    connectionStore.setSocketOpen(true)
     // Whatever happened while the socket was down was missed, so nothing
     // held in cache can be trusted to still be current.
     client?.invalidateQueries()
@@ -260,6 +260,7 @@ function connect() {
     if (socket !== ws) return
     socket = null
     liveStore.setConnected(false)
+    connectionStore.setSocketOpen(false)
     if (watchers === 0) return
     if (event.code === 1008) {
       rejected += 1
@@ -289,6 +290,8 @@ function release(onAuthFailure?: () => void) {
   socket = null
   ws?.close()
   liveStore.setConnected(false)
+  // Its `onclose` is dropped by the guard above, so say so here instead.
+  connectionStore.setSocketOpen(false)
 }
 
 /**