feat: enhance documentation with contributing guidelines and security policy

refactor: update README configuration parameters and add error handling section
refactor: streamline tonapi imports and add WalletVersion to __all__
chore: update project metadata in pyproject.toml

CONTRIBUTING.md

@@ -0,0 +1,56 @@
+# Contributing to pyfragment
+
+## Development setup
+
+```bash
+git clone https://github.com/bohd4nx/pyfragment.git
+cd pyfragment
+pip install -e ".[dev]"
+```
+
+## Running checks
+
+```bash
+# Lint and format
+ruff check . --fix && ruff format .
+
+# Type check
+mypy . --explicit-package-bases
+
+# Tests
+pytest
+```
+
+All three must pass before opening a PR.
+
+## Project structure
+
+```
+pyfragment/
+  client.py           — FragmentClient (public entry point)
+  core/               — transport, cookies, constants
+  domains/            — one package per feature domain
+    ads/              — recharge_ads, topup_ton
+    anonymous_numbers/— buy_number, manage_number
+    giveaways/        — giveaway_stars, giveaway_premium
+    marketplace/      — search_usernames, search_numbers, search_gifts
+    purchases/        — purchase_stars, purchase_premium
+    tonapi/           — wallet info, transaction signing
+  models/             — result dataclasses and enums
+  exceptions.py       — exception hierarchy
+tests/                — unit tests (pytest)
+examples/             — runnable usage examples (excluded from CI)
+```
+
+## Conventions
+
+- All public async methods live on `FragmentClient` and delegate to a domain service.
+- Domain functions receive a `FragmentClient` instance, never raw httpx clients.
+- Patch targets in tests use the module where the name is **defined**, e.g. `pyfragment.domains.tonapi.transaction.process_transaction`.
+- Versioning follows [CalVer](https://calver.org/): `YYYY.MINOR.MICRO`. Bump in `pyproject.toml`; tag as `vYYYY.MINOR.MICRO`.
+
+## Pull requests
+
+- Keep PRs focused — one feature or fix per PR.
+- Update `CHANGELOG.md` under `[Unreleased]`.
+- Add or update tests for any changed behaviour.