feat: unified context panel, remove tabs, context-aware layout

- Merged AI Assistant + Lead 360 tabs into single context-aware panel
- Context section shows: lead profile, AI insight (live from event bus), appointments, activity
- "On call with" banner only shows during active calls (isInCall prop)
- AI Chat always available at bottom of panel
- Phase 1 only — AI Chat panel needs full redesign with Vercel AI SDK tool calling (Phase 2)

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

src/components/base/avatar/base-components/avatar-count.tsx

@@ -0,0 +1,14 @@
+import { cx } from "@/utils/cx";
+
+interface AvatarCountProps {
+    count: number;
+    className?: string;
+}
+
+export const AvatarCount = ({ count, className }: AvatarCountProps) => (
+    <div className={cx("absolute right-0 bottom-0 p-px", className)}>
+        <div className="flex size-3.5 items-center justify-center rounded-full bg-fg-error-primary text-center text-[10px] leading-[13px] font-bold text-white">
+            {count}
+        </div>
+    </div>
+);