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/importers/duty_schedule.py

@@ -36,12 +36,21 @@ class DutyScheduleParseError(Exception):
 
 
 def parse_duty_schedule(raw_bytes: bytes) -> DutyScheduleResult:
-    """Parse duty-schedule JSON. Returns start_date, end_date, and list of DutyScheduleEntry.
+    """Parse duty-schedule JSON into DutyScheduleResult.
 
-    - meta.start_date (YYYY-MM-DD) and schedule (array) required.
-    - meta.weeks optional; number of days from max duty string length (split by ';').
-    - For each schedule item: name (required), duty = CSV with ';'; index i = start_date + i days.
-    - Cell value after strip: в/В/б/Б => duty, Н => unavailable, О => vacation; rest ignored.
+    Expects meta.start_date (YYYY-MM-DD) and schedule (array). For each schedule
+    item: name (required), duty string with ';' separator; index i = start_date + i days.
+    Cell values: в/В/б/Б => duty, Н => unavailable, О => vacation; rest ignored.
+
+    Args:
+        raw_bytes: UTF-8 encoded JSON bytes.
+
+    Returns:
+        DutyScheduleResult with start_date, end_date, and entries (per-person dates).
+
+    Raises:
+        DutyScheduleParseError: On invalid JSON, missing/invalid meta or schedule,
+            or invalid item fields.
     """
     try:
         data = json.loads(raw_bytes.decode("utf-8"))