feat: add rent-due share page for rent payment information

Created a new /share/rent-due/ page to display rent payment information
separately from utility bills.

Changes:
- Created /share/rent-due/[id]/ page structure with RentViewPage component
- Created ViewRentCard component to display rent amount and payment info
- Added uploadRentProofOfPayment action for tenant proof upload
- Added translation keys for rent-specific labels (en/hr)
- Updated rent email templates to link to /share/rent-due/ instead of /share/bills-due/
- Updated documentation to reflect new URL structure

The rent page displays:
- Rent amount
- IBAN or Revolut payment information with QR/barcode
- Rent proof of payment upload (when enabled)

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

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

web-app/app/lib/actions/locationActions.ts

@@ -784,6 +784,103 @@ export const uploadUtilBillsProofOfPayment = async (
     }
 }
 
+/**
+ * Upload rent proof of payment (for tenants via share link)
+ * Similar to uploadUtilBillsProofOfPayment but for rent payments
+ */
+export const uploadRentProofOfPayment = async (
+    shareId: string,
+    formData: FormData,
+    ipAddress?: string
+): Promise<{ success: boolean; error?: string }> => {
+
+    unstable_noStore();
+
+    try {
+        // 1. EXTRACT AND VALIDATE CHECKSUM (stateless, fast)
+        const extracted = extractShareId(shareId);
+        if (!extracted) {
+            console.log('shareID extraction failed');
+            return { success: false, error: 'Invalid share link' };
+        }
+
+        const { locationId: locationID, checksum } = extracted;
+
+        if (!validateShareChecksum(locationID, checksum)) {
+            console.log('shareID checksum validation failed');
+            return { success: false, error: 'Invalid share link' };
+        }
+
+        // 2. RATE LIMITING (per IP)
+        if (ipAddress) {
+            const rateLimit = checkUploadRateLimit(ipAddress);
+            if (!rateLimit.allowed) {
+                return {
+                    success: false,
+                    error: `Too many uploads. Try again in ${Math.ceil(rateLimit.resetIn / 60)} minutes.`
+                };
+            }
+        }
+
+        // 3. DATABASE VALIDATION
+        const dbClient = await getDbClient();
+
+        const location = await dbClient.collection<BillingLocation>("lokacije")
+            .findOne({ _id: locationID }, { projection: { userId: 1, rentProofOfPayment: 1, shareTTL: 1 } });
+
+        if (!location || !location.userId) {
+            return { success: false, error: 'Invalid request' };
+        }
+
+        // Check sharing is active and not expired
+        if (!location.shareTTL || new Date() > location.shareTTL) {
+            return { success: false, error: 'This content is no longer shared' };
+        }
+
+        // Check if proof of payment already uploaded
+        if (location.rentProofOfPayment) {
+            return { success: false, error: 'Proof of payment already uploaded for this location' };
+        }
+
+        // 4. FILE VALIDATION
+        const file = formData.get('rentProofOfPayment') as File;
+
+        if (!file || file.size === 0) {
+            return { success: false, error: 'No file provided' };
+        }
+
+        // Validate PDF content (magic bytes, not just MIME type)
+        const pdfValidation = await validatePdfFile(file);
+        if (!pdfValidation.valid) {
+            return { success: false, error: pdfValidation.error };
+        }
+
+        // 5. SERIALIZE & STORE FILE
+        const attachment = await serializeAttachment(file);
+
+        if (!attachment) {
+            return { success: false, error: 'Failed to process file' };
+        }
+
+        // 6. UPDATE DATABASE
+        await dbClient.collection<BillingLocation>("lokacije")
+            .updateOne(
+                { _id: locationID },
+                { $set: {
+                    rentProofOfPayment: attachment
+                } }
+            );
+
+        // 7. REVALIDATE CACHE
+        revalidatePath(`/share/rent-due/${shareId}`, 'page');
+
+        return { success: true };
+    } catch (error: any) {
+        console.error('Upload error:', error);
+        return { success: false, error: 'Upload failed. Please try again.' };
+    }
+}
+
 /**
  * Generate/activate share link for location
  * Called when owner clicks "Share" button