Add drf-spectacular for OpenAPI schema generation

Closes #2fddd5d0-1138-4a6e-96b7-5879035f033f

drf-spectacular provides OpenAPI 3.0 schema generation for all 52
registered ViewSet endpoints under api/v1/. This is a prerequisite for
auto-generating the Kotlin networking layer.

Changes:
- Add drf-spectacular dependency (0.27.x)
- Register in INSTALLED_APPS and configure DEFAULT_SCHEMA_CLASS
- Add /api/schema/ (OpenAPI YAML) and /api/docs/ (Swagger UI) routes
- Add SPECTACULAR_SETTINGS with enum name overrides to suppress warnings

Schema generates cleanly with 4 non-blocking warnings (1 unique:
TagListSerializerField defaulting to string) and 14 unique skipped
errors (all non-ViewSet APIViews like webhooks that lack serializers).

poetry.lock

@@ -1657,6 +1657,30 @@ files = [
 [package.dependencies]
 django = ">=4.2"
 
+[[package]]
+name = "drf-spectacular"
+version = "0.27.2"
+description = "Sane and flexible OpenAPI 3 schema generation for Django REST framework"
+optional = false
+python-versions = ">=3.7"
+groups = ["main"]
+files = [
+    {file = "drf-spectacular-0.27.2.tar.gz", hash = "sha256:a199492f2163c4101055075ebdbb037d59c6e0030692fc83a1a8c0fc65929981"},
+    {file = "drf_spectacular-0.27.2-py3-none-any.whl", hash = "sha256:b1c04bf8b2fbbeaf6f59414b4ea448c8787aba4d32f76055c3b13335cf7ec37b"},
+]
+
+[package.dependencies]
+Django = ">=2.2"
+djangorestframework = ">=3.10.3"
+inflection = ">=0.3.1"
+jsonschema = ">=2.6.0"
+PyYAML = ">=5.1"
+uritemplate = ">=2.0.0"
+
+[package.extras]
+offline = ["drf-spectacular-sidecar"]
+sidecar = ["drf-spectacular-sidecar"]
+
 [[package]]
 name = "dulwich"
 version = "0.24.1"
@@ -4915,7 +4939,7 @@ version = "6.0.3"
 description = "YAML parser and emitter for Python"
 optional = false
 python-versions = ">=3.8"
-groups = ["test"]
+groups = ["main", "test"]
 files = [
     {file = "PyYAML-6.0.3-cp38-cp38-macosx_10_13_x86_64.whl", hash = "sha256:c2514fceb77bc5e7a2f7adfaa1feb2fb311607c9cb518dbc378688ec73d8292f"},
     {file = "PyYAML-6.0.3-cp38-cp38-manylinux2014_aarch64.manylinux_2_17_aarch64.manylinux_2_28_aarch64.whl", hash = "sha256:9c57bb8c96f6d1808c030b1687b9b5fb476abaa47f0db9c0101f5e9f394e97f4"},
@@ -6872,4 +6896,4 @@ cffi = ["cffi (>=1.17,<2.0) ; platform_python_implementation != \"PyPy\" and pyt
 [metadata]
 lock-version = "2.1"
 python-versions = ">=3.11,<3.15"
-content-hash = "fe85397f7562cd1b81cdf7ab6c82ccab64d760310264e95944de9219731c9ee6"
+content-hash = "a40297d1cdc081a926b8189bd1e284a5eb83462e218dc8d17b56dd9679baeea4"