feat: add floating call widget with SIP controls, click-to-call, and SIP provider

Introduce a shared SipProvider context so all components use the same SIP
connection. Add a floating CallWidget (idle pill, ringing, active with
disposition, ended states) visible for CC agents on every page. Add a
ClickToCallButton for the worklist. Wire SIP status badge and worklist
into the call-desk page.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/providers/sip-provider.tsx

@@ -0,0 +1,26 @@
+import { createContext, useContext, useEffect, type PropsWithChildren } from 'react';
+import { useSipPhone } from '@/hooks/use-sip-phone';
+
+type SipContextType = ReturnType<typeof useSipPhone>;
+
+const SipContext = createContext<SipContextType | null>(null);
+
+export const SipProvider = ({ children }: PropsWithChildren) => {
+    const sipPhone = useSipPhone();
+
+    // Auto-connect on mount
+    useEffect(() => {
+        sipPhone.connect();
+        // eslint-disable-next-line react-hooks/exhaustive-deps
+    }, []);
+
+    return <SipContext.Provider value={sipPhone}>{children}</SipContext.Provider>;
+};
+
+export const useSip = (): SipContextType => {
+    const ctx = useContext(SipContext);
+    if (ctx === null) {
+        throw new Error('useSip must be used within a SipProvider');
+    }
+    return ctx;
+};