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/admin/schemas.py

@@ -0,0 +1,46 @@
+from typing import Literal
+
+from pydantic import BaseModel, EmailStr, Field, field_validator
+
+from app.core.password_policy import validate_password_strength
+
+
+class AdminUserPatchIn(BaseModel):
+    role: Literal["user", "admin"] | None = None
+    status: Literal["pending", "active", "blocked"] | None = None
+    is_superuser: bool | None = None
+
+
+class AdminUserCreateIn(BaseModel):
+    email: EmailStr
+    password: str = Field(min_length=8)
+    role: Literal["user", "admin"] = "user"
+    is_superuser: bool = False
+    status: Literal["pending", "active", "blocked"] = "active"
+
+    @field_validator("password")
+    @classmethod
+    def password_policy(cls, value: str) -> str:
+        return validate_password_strength(value)
+
+
+class AdminUserPasswordPatchIn(BaseModel):
+    password: str = Field(min_length=8)
+
+    @field_validator("password")
+    @classmethod
+    def password_policy(cls, value: str) -> str:
+        return validate_password_strength(value)
+
+
+class AdminSettingsPatchIn(BaseModel):
+    values: dict
+
+
+class AdminUiActivityIn(BaseModel):
+    event: str
+    meta: dict | None = None
+
+
+class AdminRevealSecretIn(BaseModel):
+    key: Literal["database_password", "jwt_access_secret", "jwt_refresh_pepper", "s3_secret_key"]