docs: add repo agent rules

Author: bachnxuan

AGENTS.md

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+- ALWAYS read `README.md`, `config.sh`, `justfile`, `build.sh`, `build/`, `ci/`, `py/pyproject.toml`, and `.github/workflows/` before changing script behavior.
+- Keep behavior wiring in the usual places: top-level flow in `build.sh`, defaults and repo settings in `config.sh`, build steps in `build/`, packaging and Telegram logic in `ci/`, and API/JSON helper code in `py/`.
+- PREFER Bash for orchestration, patching, packaging, and filesystem work. PREFER Python for API calls, JSON handling, Telegram requests, release metadata, and the helper CLI.
+- ALWAYS use the existing `py_cli` wrapper when Bash needs the Python helper package.
+- Keep Python changes inside the uv-managed `py/` project and stay on Python 3.14.
+- ALWAYS use the existing boolean conventions. `STOCK_CONFIG` stays `auto`, `true`, or `false`, and invalid boolean-like values should fail clearly.
+- PREFER the existing log helpers instead of ad hoc output.
+- AVOID moving build orchestration into Python.
+- AVOID adding a new function unless it is needed and reused. If the behavior fits cleanly in an existing function, add it there.
+- AVOID adding new wrappers or helper layers when the existing Bash or Python entry points already fit the job.
+- AVOID broad cleanup or refactor edits outside the part of the build flow you are changing.
+- Run the relevant checks for what you changed: `just fmt-check`, `just bash-check`, `just lint`, `just py-lint`, `just py-check`, or `just check`.
+- NEVER add frontend, Windows, or macOS tooling. This repo is Linux-only Bash plus Python.
+- AVOID editing generated or downloaded paths unless the task is explicitly about build artifacts or local cache handling: `out/`, `work/`, `boot_image/`, `clang/`, `kernel/`, `anykernel3/`, `build-tools/`, `mkbootimg/`, `susfs/`, `libfakestat/`, `.ccache/`, `build/clang`, and `build/ld.lld`.
+- Keep `.gitignore` focused on actual generated paths in this repo. PREFER concrete directories and files over broad extension globs.
+- AVOID adding ignores for frontend, Windows, macOS, coverage, or generic archive/object patterns unless the repo actually starts generating them.
+- Keep workflow inputs and defaults aligned with `config.sh` and the build scripts, especially target-specific defaults and `STOCK_CONFIG=auto`.
+- AVOID changing workflow inputs, defaults, or env names without updating the matching Bash handling.
+- ALWAYS use conventional commit style. Keep scopes short, like `py` or `build`, not full paths like `py/src/tools`. Omit the scope for treewide changes.
+- ALWAYS update `README.md` when behavior, commands, inputs, outputs, or setup steps change.