… interface

Renamed _Config to Config and added it to the public API (`__all__`).

Added `update()` and `clear_overrides()` for in-memory runtime overrides.

Updated `get()` to respect overrides before user config and defaults.

Introduced `_SENSITIVE_KEYS` tuple and masked sensitive values in `__str__` and `__repr__`.

Marked `set()`, `remove()`, and `save()` as [INTERNAL USE ONLY] in docstrings.

Clarified resolution priority in class and method docstrings.

Updated `vertopal.api.interface` to import and use `Config` instead of `_Config`.

Updated `vertopal.cli.config_manager` to import and use `Config`, and adjusted docstrings to reference internal methods.

Exposed `Config` at the top-level in `vertopal/__init__.py` for external usage.

Added CHANGELOG entry under Unreleased documenting new Config features.

Rewind file streams before upload to prevent EMPTY_FILE errors and truncated uploads.

Added __len__, __iter__, and __next__ magic methods to improve compatibility with streaming clients
and support chunk iteration.

Added CHANGELOG entry under Unreleased documenting _ChunkedFileWrapper fixes.

…, DisabledForFreeApp, WrongFormatStructure, InvalidFormat)

Updated CHANGELOG to document new exceptions.