feat(phase1): add image storage utilities

- Create backend/services/image_storage.py with 4 core functions:
  - sanitize_filename(): remove unsafe chars, limit to 255 chars, convert to lowercase
  - get_unique_filename(): handle collisions with UUID suffix (format: {name}_{uuid8}_{variant}.jpg)
  - ensure_image_directories(): create /images/ root and category subdirs on startup
  - save_image(): save bytes to /images/{category}/{filename}, returns relative path
- Create comprehensive test suite (22 tests) covering all functionality
- Integrate ensure_image_directories() into FastAPI startup event
- Directory structure: /images/{category}/{filename}
- Collision handling: auto-suffix with UUID if filename exists
- All tests passing, pathlib.Path for safe operations

venv/lib/python3.12/site-packages/greenlet/TBrokenGreenlet.cpp

@@ -0,0 +1,45 @@
+/* -*- indent-tabs-mode: nil; tab-width: 4; -*- */
+/**
+ * Implementation of greenlet::UserGreenlet.
+ *
+ * Format with:
+ *  clang-format -i --style=file src/greenlet/greenlet.c
+ *
+ *
+ * Fix missing braces with:
+ *   clang-tidy src/greenlet/greenlet.c -fix -checks="readability-braces-around-statements"
+*/
+
+#include "TGreenlet.hpp"
+
+namespace greenlet {
+
+void* BrokenGreenlet::operator new(size_t UNUSED(count))
+{
+    return allocator.allocate(1);
+}
+
+
+void BrokenGreenlet::operator delete(void* ptr)
+{
+    return allocator.deallocate(static_cast<BrokenGreenlet*>(ptr),
+                                1);
+}
+
+greenlet::PythonAllocator<greenlet::BrokenGreenlet> greenlet::BrokenGreenlet::allocator;
+
+bool
+BrokenGreenlet::force_slp_switch_error() const noexcept
+{
+    return this->_force_slp_switch_error;
+}
+
+UserGreenlet::switchstack_result_t BrokenGreenlet::g_switchstack(void)
+{
+  if (this->_force_switch_error) {
+    return switchstack_result_t(-1);
+  }
+  return UserGreenlet::g_switchstack();
+}
+
+}; //namespace greenlet