docs: Update AGENTS.md for Feature 5 (PDF Merge) completion

- Update test count: 82 passed, 7 skipped (was 62 passed)
- Update PdfOperationsController status: Partial (1/N endpoints), 7 tests
- Add PdfOperationsController Status section with merge endpoint details
- Mark merge endpoint as DONE (Phase 1, Priority 5)
- List remaining Phase 2 endpoints: stamp, annotate

AGENTS.md

@@ -188,7 +188,7 @@ After completing all Phase 1-3 controllers (PdfValidation, PdfAttachment, SwissQ
 dotnet build
 ```
 
-**Run tests (62 passed, 7 skipped as of Feature 4 - PDF Attachment Extraction):**
+**Run tests (82 passed, 7 skipped as of Feature 5 - PDF Merge):**
 ```powershell
 dotnet test
 ```
@@ -276,7 +276,7 @@ Do NOT add `if (result.IsSuccess)` checks. Throw exceptions for errors. The midd
 | **PdfValidationController** | ✅ DONE | 13 (7 validate + 6 validate-pdfa) |
 | **SwissQrCodeController** | ✅ DONE | 2 |
 | **PdfAttachmentController** | ⏳ Partial (2/3 endpoints) | 10 (4 check + 6 extract) |
-| **PdfOperationsController** | ⏳ Pending | 0 |
+| **PdfOperationsController** | ⏳ Partial (1/N endpoints) | 7 (merge endpoint only) |
 | **PdfConversionController** | ⏳ Pending | 0 |
 
 **PdfAttachmentController Status:**
@@ -284,6 +284,11 @@ Do NOT add `if (result.IsSuccess)` checks. Throw exceptions for errors. The midd
 - ✅ `POST /api/pdf/attachments/extract` - DONE (Phase 1, Priority 4) - Returns ZIP with all attachments
 - ⏳ `POST /api/pdf/attachments/add` - TODO (Phase 2, Priority 7)
 
+**PdfOperationsController Status:**
+- ✅ `POST /api/pdf/operations/merge` - DONE (Phase 1, Priority 5) - Merges multiple PDFs with optional page ranges (multipart + Base64)
+- ⏳ `POST /api/pdf/operations/stamp` - TODO (Phase 2, Priority 6)
+- ⏳ `POST /api/pdf/operations/annotate` - TODO (Phase 2, Priority 6)
+
 **Note:** PdfRenderController removed - moved to .NET client library.
 
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