feat(sidebar): add interactive drag-to-open gesture

Sidebar now follows the finger during swipe-to-open gesture from anywhere
on the screen. Uses shared animation context between AppContainer and
SlidingSidebar for synchronized translateX values.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/app/src/contexts/sidebar-animation-context.tsx

@@ -0,0 +1,117 @@
+import { createContext, useContext, useEffect, useRef, type ReactNode } from "react";
+import { useWindowDimensions } from "react-native";
+import {
+  useSharedValue,
+  withTiming,
+  Easing,
+  type SharedValue,
+} from "react-native-reanimated";
+import { useSidebarStore } from "@/stores/sidebar-store";
+
+const ANIMATION_DURATION = 220;
+const ANIMATION_EASING = Easing.bezier(0.25, 0.1, 0.25, 1);
+
+interface SidebarAnimationContextValue {
+  translateX: SharedValue<number>;
+  backdropOpacity: SharedValue<number>;
+  windowWidth: number;
+  animateToOpen: () => void;
+  animateToClose: () => void;
+  isGesturing: SharedValue<boolean>;
+}
+
+const SidebarAnimationContext = createContext<SidebarAnimationContextValue | null>(null);
+
+export function SidebarAnimationProvider({ children }: { children: ReactNode }) {
+  const { width: windowWidth } = useWindowDimensions();
+  const { isOpen } = useSidebarStore();
+
+  // Initialize based on current state
+  const translateX = useSharedValue(isOpen ? 0 : -windowWidth);
+  const backdropOpacity = useSharedValue(isOpen ? 1 : 0);
+  const isGesturing = useSharedValue(false);
+
+  // Track previous isOpen to detect changes
+  const prevIsOpen = useRef(isOpen);
+
+  // Sync animation with store state changes (e.g., backdrop tap, programmatic open/close)
+  useEffect(() => {
+    // Skip if this is initial render or if we're mid-gesture
+    if (prevIsOpen.current === isOpen) {
+      return;
+    }
+    prevIsOpen.current = isOpen;
+
+    // Don't animate if we're in the middle of a gesture - the gesture handler will handle it
+    if (isGesturing.value) {
+      return;
+    }
+
+    if (isOpen) {
+      translateX.value = withTiming(0, {
+        duration: ANIMATION_DURATION,
+        easing: ANIMATION_EASING,
+      });
+      backdropOpacity.value = withTiming(1, {
+        duration: ANIMATION_DURATION,
+        easing: ANIMATION_EASING,
+      });
+    } else {
+      translateX.value = withTiming(-windowWidth, {
+        duration: ANIMATION_DURATION,
+        easing: ANIMATION_EASING,
+      });
+      backdropOpacity.value = withTiming(0, {
+        duration: ANIMATION_DURATION,
+        easing: ANIMATION_EASING,
+      });
+    }
+  }, [isOpen, translateX, backdropOpacity, windowWidth, isGesturing]);
+
+  const animateToOpen = () => {
+    "worklet";
+    translateX.value = withTiming(0, {
+      duration: ANIMATION_DURATION,
+      easing: ANIMATION_EASING,
+    });
+    backdropOpacity.value = withTiming(1, {
+      duration: ANIMATION_DURATION,
+      easing: ANIMATION_EASING,
+    });
+  };
+
+  const animateToClose = () => {
+    "worklet";
+    translateX.value = withTiming(-windowWidth, {
+      duration: ANIMATION_DURATION,
+      easing: ANIMATION_EASING,
+    });
+    backdropOpacity.value = withTiming(0, {
+      duration: ANIMATION_DURATION,
+      easing: ANIMATION_EASING,
+    });
+  };
+
+  return (
+    <SidebarAnimationContext.Provider
+      value={{
+        translateX,
+        backdropOpacity,
+        windowWidth,
+        animateToOpen,
+        animateToClose,
+        isGesturing,
+      }}
+    >
+      {children}
+    </SidebarAnimationContext.Provider>
+  );
+}
+
+export function useSidebarAnimation() {
+  const context = useContext(SidebarAnimationContext);
+  if (!context) {
+    throw new Error("useSidebarAnimation must be used within SidebarAnimationProvider");
+  }
+  return context;
+}