chore: add changelog and documentation updates

- Created a new `CHANGELOG.md` file to document all notable changes to the project, adhering to the Keep a Changelog format.
- Updated `CONTRIBUTING.md` to include instructions for building and previewing documentation using MkDocs.
- Added `mkdocs.yml` configuration for documentation generation, including navigation structure and theme settings.
- Enhanced various documentation files, including API reference, architecture overview, configuration reference, and runbook, to provide comprehensive guidance for users and developers.
- Included new sections in the README for changelog and documentation links, improving accessibility to project information.

duty_teller/db/schemas.py

@@ -1,4 +1,4 @@
-"""Pydantic schemas for API and validation."""
+"""Pydantic schemas for API request/response and validation."""
 
 from typing import Literal
 
@@ -6,6 +6,8 @@ from pydantic import BaseModel, ConfigDict
 
 
 class UserBase(BaseModel):
+    """Base user fields (full_name, username, first/last name)."""
+
     full_name: str
     username: str | None = None
     first_name: str | None = None
@@ -13,10 +15,14 @@ class UserBase(BaseModel):
 
 
 class UserCreate(UserBase):
+    """User creation payload including Telegram user id."""
+
     telegram_user_id: int
 
 
 class UserInDb(UserBase):
+    """User as stored in DB (includes id and telegram_user_id)."""
+
     id: int
     telegram_user_id: int
 
@@ -24,16 +30,22 @@ class UserInDb(UserBase):
 
 
 class DutyBase(BaseModel):
+    """Duty fields: user_id, start_at, end_at (UTC ISO 8601 with Z)."""
+
     user_id: int
     start_at: str  # UTC, ISO 8601 with Z
     end_at: str  # UTC, ISO 8601 with Z
 
 
 class DutyCreate(DutyBase):
+    """Duty creation payload."""
+
     pass
 
 
 class DutyInDb(DutyBase):
+    """Duty as stored in DB (includes id)."""
+
     id: int
 
     model_config = ConfigDict(from_attributes=True)