Initial commit: pwweb - PipeWire WebUI

C++ backend with SSE streaming (reuses qpwgraph PipeWire callbacks).
Svelte frontend with custom SVG canvas for port-level connections.

Features:
- Live PipeWire graph via SSE
- Drag output->input port to connect
- Double-click or select+Delete to disconnect
- Node positions saved to localStorage
- Pan (drag bg) and zoom (scroll)
- Port type coloring (audio=green, midi=red, video=blue)

frontend/src/lib/stores.ts

@@ -0,0 +1,64 @@
+import { writable, derived, get } from 'svelte/store';
+import type { Node, Port, Link, GraphMessage } from './types';
+import { subscribe, connectPorts, disconnectPorts } from './ws';
+
+// Raw graph stores
+export const nodes = writable<Node[]>([]);
+export const ports = writable<Port[]>([]);
+export const links = writable<Link[]>([]);
+export const connected = writable(false);
+
+// Port lookup map
+export const portById = derived(ports, ($ports) => {
+  const map = new Map<number, Port>();
+  for (const p of $ports) map.set(p.id, p);
+  return map;
+});
+
+// Node lookup map
+export const nodeById = derived(nodes, ($nodes) => {
+  const map = new Map<number, Node>();
+  for (const n of $nodes) map.set(n.id, n);
+  return map;
+});
+
+// Initialize: fetch via REST immediately, then subscribe to WS for updates
+let unsubscribe: (() => void) | null = null;
+
+function applyGraph(graph: GraphMessage) {
+  nodes.set(graph.nodes);
+  ports.set(graph.ports);
+  links.set(graph.links);
+  connected.set(true);
+}
+
+export async function initGraph() {
+  if (unsubscribe) return;
+
+  // 1. Fetch initial state via REST API (works immediately, no WS needed)
+  try {
+    const res = await fetch('/api/graph');
+    if (res.ok) {
+      const graph: GraphMessage = await res.json();
+      applyGraph(graph);
+    }
+  } catch (e) {
+    console.warn('[graph] REST fetch failed:', e);
+  }
+
+  // 2. Subscribe to WebSocket for live updates
+  unsubscribe = subscribe((graph: GraphMessage) => {
+    applyGraph(graph);
+  });
+}
+
+export function destroyGraph() {
+  if (unsubscribe) {
+    unsubscribe();
+    unsubscribe = null;
+    connected.set(false);
+  }
+}
+
+// Re-export connection functions
+export { connectPorts, disconnectPorts };