[BUG]: Reset password form shows generic "Password update failed" instead of the backend's specific error (e.g. expired code)

### Bug Description

On the Reset Password form, when the backend rejects a reset attempt (e.g. an expired or invalid reset code), the form always shows the generic message **"Password update failed"** instead of the specific reason the backend returned (e.g. "Reset code has expired. Please request a new one.").

**Root cause** — field-name mismatch in `frontend/src/context/authContext.tsx` (`confirmForgotPassword`, line ~294):
```js
if (!response.ok) {
const data = await response.json();
throw new Error(data.message || 'Password update failed');
}
```
The backend returns its error under the `error` field (e.g. `{"error": "Reset code has expired. Please request a new one."}`), but the frontend reads `data.message`. Since `message` is absent, it always falls back to the generic string.

**Fix:** read `data.error` (with a sensible fallback), e.g.:
```js
throw new Error(data.error || data.message || 'Password update failed');
```

This is the same class of issue as #470 (auth errors not surfaced due to inconsistent response fields), scoped here to the reset-password flow.

cc @Ri1tik — could you assign this to me? I'm already working on the related reset-code expiry fix (#485), and the backend there returns a clear "Reset code has expired" message that this frontend change would surface properly.

### Steps to Reproduce

1. Trigger a reset failure — e.g. request a password reset code, then submit it after it's invalid/expired (or enter a wrong code).
2. The backend responds with 400 and `{"error": ""}`.
3. Observe the form displays "Password update failed" instead of the specific reason from the backend.

### Logs and Screenshots

frontend/src/context/authContext.tsx (~line 294):
throw new Error(data.message || 'Password update failed');
// backend sends { "error": "..." }, not { "message": "..." } → always falls back

### Environment Details

- File: frontend/src/context/authContext.tsx (confirmForgotPassword, ~line 294)
- Page: Reset Password form (/auth)
- Frontend: Vite + React
- Branch: main
- Related: #470 (same class — inconsistent response field); surfaces alongside #485 (reset-code expiry)

### Impact

Low - Minor inconvenience

### Code of Conduct

- [x] I have joined the [Discord server](https://discord.gg/hjUhu33uAn) and will post updates there
- [x] I have searched existing issues to avoid duplicates