Update admin theme/layout and refresh README details.

Align the project baseline with the latest admin interface styling and layout structure while documenting setup and usage updates in README.

apps/api/app/modules/content/schemas.py

@@ -0,0 +1,24 @@
+from typing import Literal
+
+from pydantic import BaseModel, Field
+
+
+class ContentPageIn(BaseModel):
+    slug: str = Field(min_length=2, max_length=120)
+    title: str = Field(min_length=2, max_length=200)
+    body: str
+    status: Literal["draft", "published"] = "draft"
+
+
+class ContentPagePatchIn(BaseModel):
+    title: str | None = Field(default=None, min_length=2, max_length=200)
+    body: str | None = None
+    status: Literal["draft", "published"] | None = None
+
+
+class ContentPageOut(BaseModel):
+    id: str
+    slug: str
+    title: str
+    body: str
+    status: str