chore: update Python version to 3.11 in CI and project files; remove outdated CONTRIBUTING and SECURITY documents

CONTRIBUTING.md

@@ -1,58 +0,0 @@
-# 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)
-  enums.py            — ApiProvider, PaymentMethod, WalletVersion
-  exceptions.py       — exception hierarchy
-  core/               — constants, validation helpers
-  domains/            — one package per feature domain
-    ads/              — recharge_ads, topup_gram
-    anonymous_numbers/— get_login_code, toggle_login_codes, terminate_sessions
-    giveaways/        — giveaway_stars, giveaway_premium
-    marketplace/      — search_usernames, search_numbers, search_gifts
-    purchases/        — purchase_stars, purchase_premium
-  services/           — shared infrastructure services
-    cookies/          — browser cookie extraction (models + service)
-    tonapi/           — wallet info, transaction signing (tonapi/toncenter)
-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.services.tonapi.transaction._make_ton_client`.
-- 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.