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/pyasn1_modules/rfc4985.py

@@ -0,0 +1,49 @@
+#
+# This file is part of pyasn1-modules software.
+#
+# Created by Russ Housley.
+#
+# Copyright (c) 2019, Vigil Security, LLC
+# License: http://snmplabs.com/pyasn1/license.html
+#
+# Expression of Service Names in X.509 Certificates
+#
+# ASN.1 source from:
+# https://www.rfc-editor.org/rfc/rfc4985.txt
+#
+
+from pyasn1.type import char
+from pyasn1.type import constraint
+from pyasn1.type import univ
+
+from pyasn1_modules import rfc5280
+
+MAX = float('inf')
+
+
+# As specified in Appendix A.2 of RFC 4985
+
+id_pkix = rfc5280.id_pkix
+
+id_on = id_pkix + (8, )
+
+id_on_dnsSRV = id_on + (7, )
+
+
+class SRVName(char.IA5String):
+    subtypeSpec = constraint.ValueSizeConstraint(1, MAX)
+
+
+srvName = rfc5280.AnotherName()
+srvName['type-id'] = id_on_dnsSRV
+srvName['value'] = SRVName()
+
+
+# Map of Other Name OIDs to Other Name is added to the
+# ones that are in rfc5280.py
+
+_anotherNameMapUpdate = {
+    id_on_dnsSRV: SRVName(),
+}
+
+rfc5280.anotherNameMap.update(_anotherNameMapUpdate)