fix: Add useBackToNewChat Hook for Back Navigation Handling

- Introduced a new hook `useBackToNewChat` to manage state when navigating back to the `/c/new` route.
- The hook listens for browser back/forward navigation events and resets the conversation state appropriately.
- Integrated the hook into `ChatRoute.tsx` to ensure proper functionality during navigation.
- Added documentation detailing the problem, solution, and implementation of the new hook.

docs/fixes/back-button-navigation-fix.md

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+# Back Button Navigation Fix for LibreChat
+
+## Problem
+When users navigate back to `/c/new` using the browser's back button from an existing conversation, the conversation state doesn't reset properly. This causes new messages to be appended to the previous conversation instead of creating a new one.
+
+## Solution
+Created a custom hook `useBackToNewChat` that listens for browser back/forward navigation events and resets the conversation state when navigating back to `/c/new`.
+
+## Implementation
+
+### New Hook: `useBackToNewChat`
+Located at: `client/src/hooks/useBackToNewChat.ts`
+
+The hook:
+1. **Listens to popstate events** - Detects when users use browser back/forward buttons
+2. **Checks current path** - Verifies if the navigation landed on `/c/new`
+3. **Resets conversation state** - Clears messages and creates a new conversation if needed
+
+### Integration
+The hook is used in `ChatRoute.tsx`:
+```typescript
+// Handle back navigation to /c/new
+useBackToNewChat(index);
+```
+
+## Why This Approach?
+- **Direct browser event handling** - The `popstate` event fires specifically for browser navigation (back/forward buttons)
+- **No complex state tracking** - Avoids finicky effects that depend on conversation state changes
+- **Simple and focused** - Single responsibility: detect back navigation to new chat and reset state
+
+## Benefits
+- Minimal impact on existing code
+- Isolated logic that's easier to test and maintain
+- Directly addresses the root cause (browser back button)
+- Avoids race conditions with conversation state updates
+
+## Testing
+Test file: `client/src/hooks/__tests__/useBackToNewChat.test.ts`
+
+Tests cover:
+- Popstate event handling when navigating to /c/new
+- No action when already on /c/new
+- No action when navigating to other routes