fix: improve note interactions and markdown LaTeX support

## Bug Fixes

### Note Card Actions
- Fix broken size change functionality (missing state declaration)
- Implement React 19 useOptimistic for instant UI feedback
- Add startTransition for non-blocking updates
- Ensure smooth animations without page refresh
- All note actions now work: pin, archive, color, size, checklist

### Markdown LaTeX Rendering
- Add remark-math and rehype-katex plugins
- Support inline equations with dollar sign syntax
- Support block equations with double dollar sign syntax
- Import KaTeX CSS for proper styling
- Equations now render correctly instead of showing raw LaTeX

## Technical Details

- Replace undefined currentNote references with optimistic state
- Add optimistic updates before server actions for instant feedback
- Use router.refresh() in transitions for smart cache invalidation
- Install remark-math, rehype-katex, and katex packages

## Testing

- Build passes successfully with no TypeScript errors
- Dev server hot-reloads changes correctly

keep-notes/app/actions/auth-reset.ts

@@ -0,0 +1,86 @@
+'use server'
+
+import prisma from '@/lib/prisma'
+import { sendEmail } from '@/lib/mail'
+import bcrypt from 'bcryptjs'
+import { getEmailTemplate } from '@/lib/email-template'
+
+// Helper simple pour générer un token sans dépendance externe lourde
+function generateToken() {
+  const array = new Uint8Array(32);
+  globalThis.crypto.getRandomValues(array);
+  return Array.from(array, byte => byte.toString(16).padStart(2, '0')).join('');
+}
+
+export async function forgotPassword(email: string) {
+  if (!email) return { error: "Email is required" };
+
+  try {
+    const user = await prisma.user.findUnique({ where: { email: email.toLowerCase() } });
+    if (!user) {
+      // Pour des raisons de sécurité, on ne dit pas si l'email existe ou pas
+      return { success: true }; 
+    }
+
+    const token = generateToken();
+    const expiry = new Date(Date.now() + 3600000); // 1 hour
+
+    await prisma.user.update({
+      where: { id: user.id },
+      data: {
+        resetToken: token,
+        resetTokenExpiry: expiry
+      }
+    });
+
+    const resetLink = `${process.env.NEXTAUTH_URL || 'http://localhost:3000'}/reset-password?token=${token}`;
+
+    const html = getEmailTemplate(
+      "Reset your Password",
+      "<p>You requested a password reset for your Memento account.</p><p>Click the button below to set a new password. This link is valid for 1 hour.</p>",
+      resetLink,
+      "Reset Password"
+    );
+
+    await sendEmail({
+      to: user.email,
+      subject: "Reset your Memento password",
+      html
+    });
+
+    return { success: true };
+  } catch (error) {
+    console.error('Forgot password error:', error);
+    return { error: "Failed to send reset email" };
+  }
+}
+
+export async function resetPassword(token: string, newPassword: string) {
+  if (!token || !newPassword) return { error: "Missing token or password" };
+
+  try {
+    const user = await prisma.user.findUnique({
+      where: { resetToken: token }
+    });
+
+    if (!user || !user.resetTokenExpiry || user.resetTokenExpiry < new Date()) {
+      return { error: "Invalid or expired token" };
+    }
+
+    const hashedPassword = await bcrypt.hash(newPassword, 10);
+
+    await prisma.user.update({
+      where: { id: user.id },
+      data: {
+        password: hashedPassword,
+        resetToken: null,
+        resetTokenExpiry: null
+      }
+    });
+
+    return { success: true };
+  } catch (error) {
+    console.error('Reset password error:', error);
+    return { error: "Failed to reset password" };
+  }
+}