Add AGENTS/CLAUDE contributor instructions for dev-3.x (#1767)

* Add AGENTS and CLAUDE contributor guidance

* Update AGENTS.md to include code style enforcement via Ruff

* Remove unnecessary AGENTS.md guidance

AGENTS.md

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+# AGENTS.md
+
+This file defines how coding agents should contribute to `aiogram` on `dev-3.x`.
+
+## Scope and defaults
+
+- Base branch: `dev-3.x`
+- Python: `>=3.10`
+- Main tooling: `uv`, `ruff`, `mypy`, `pytest`, `towncrier`, `butcher`
+- Keep diffs focused; avoid unrelated refactors/reformatting.
+
+## Setup
+
+```bash
+uv sync --all-extras --group dev --group test
+uv run pre-commit install
+```
+
+Note: `uv run pre-commit install` writes hooks to the shared repository `.git/hooks`
+(common for all worktrees), not only for the current worktree.
+
+## Mandatory local checks before PR
+
+Code style/lint in this repository is enforced via Ruff (`ruff check` + `ruff format`).
+
+Quick loop (recommended for most PR iterations):
+
+```bash
+uv run ruff check --show-fixes --preview aiogram examples
+uv run ruff format --check --diff aiogram tests scripts examples
+uv run mypy aiogram
+uv run pytest tests
+```
+
+Full loop (run before final review request):
+
+```bash
+# Run quick loop first, then:
+uv run pytest --redis redis://<host>:<port>/<db> tests  # when Redis storage paths are affected
+uv run pytest --mongo mongodb://<user>:<password>@<host>:<port> tests  # when Mongo storage paths are affected
+uv run --extra docs bash -c 'cd docs && make html'  # when docs or generated API docs are affected
+```
+
+If changes touch Redis/Mongo storage behavior, run integration variants too:
+
+```bash
+uv run pytest --redis redis://<host>:<port>/<db> tests
+uv run pytest --mongo mongodb://<user>:<password>@<host>:<port> tests
+```
+
+Run these only if you have accessible Redis/Mongo instances in your environment.
+
+
+## Changelog rules (CI-gated)
+
+- Add `CHANGES/<issue-or-pr>.<category>.rst` unless PR has `skip news` label.
+- Valid categories: `feature`, `bugfix`, `doc`, `removal`, `misc`.
+- Changelog text must describe user-visible behavior changes, not process/org details.
+- Do not edit `CHANGES.rst` directly for regular PRs.
+
+## Bot API/codegen workflow (critical)
+
+`aiogram` API layers are generated. For Bot API related work:
+
+- Prefer editing generator inputs (`.butcher/**/*.yml`, aliases, templates) instead of hand-editing generated code.
+- Do not manually edit `.butcher/**/entity.json` (parser/codegen will overwrite it).
+- For new shortcuts, add alias/config in `.butcher` and regenerate.
+- Regeneration flow:
+
+```bash
+uv run --extra cli butcher parse
+uv run --extra cli butcher refresh
+uv run --extra cli butcher apply all
+```
+
+For maintainers preparing an API/version bump only:
+
+```bash
+make update-api args=patch
+```
+
+`make update-api args=...` also runs version bump scripts and updates version-related files
+(`aiogram/__meta__.py`, `README.rst`, `docs/index.rst`).
+
+After regeneration, run lint/type/tests again.
+
+## Maintainer review signals (recent PRs)
+
+These patterns repeatedly appeared in maintainer feedback and should be treated as hard constraints:
+
+- Keep generation path consistent: shortcuts/features should be added through `.butcher` config + generation, not ad-hoc manual edits.
+- Keep test style consistent with existing suite; avoid introducing new dependencies for small tests.
+- Preserve framework contracts (e.g., dispatcher/workflow data passed to startup/shutdown callbacks).
+- When fixing generated API metadata/docs, update the source mapping in `.butcher` so future regenerations keep the fix.
+
+## Documentation work
+
+For docs changes:
+
+```bash
+uv run --extra docs sphinx-autobuild --watch aiogram/ --watch CHANGES.rst --watch README.rst docs/ docs/_build/
+```
+
+`sphinx-autobuild` is long-running by design.
+
+Or quick build:
+
+```bash
+uv run --extra docs bash -c 'cd docs && make html'
+```
+
+## PR quality checklist
+
+Before requesting review:
+
+1. Tests added/updated for behavior changes.
+2. Local lint/type/tests pass.
+3. Changelog fragment added (or `skip news` is justified).
+4. If codegen-related: generated files and source config are both updated coherently.
+5. PR body includes clear reproduction/validation steps.

CLAUDE.md

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+# CLAUDE.md
+
+Use @AGENTS.md as the source of truth for contribution workflow, checks, and Bot API codegen rules in this repository.