Refactor project structure and enhance Docker configuration

- Updated `.dockerignore` to exclude test and development artifacts, optimizing the Docker image size.
- Refactored `main.py` to delegate execution to `duty_teller.run.main()`, simplifying the entry point.
- Introduced a new `duty_teller` package to encapsulate core functionality, improving modularity and organization.
- Enhanced `pyproject.toml` to define a script for running the application, streamlining the execution process.
- Updated README documentation to reflect changes in project structure and usage instructions.
- Improved Alembic environment configuration to utilize the new package structure for database migrations.

duty_teller/utils/user.py

@@ -0,0 +1,8 @@
+"""User display name helpers."""
+
+
+def build_full_name(first_name: str | None, last_name: str | None) -> str:
+    """Build display full name from first and last name. Returns 'User' if both empty."""
+    parts = [first_name or "", last_name or ""]
+    full = " ".join(filter(None, parts)).strip()
+    return full or "User"