docs: add LICENSE, CONTRIBUTING, and CHANGELOG

- LICENSE: MIT, retaining the original behavior3 copyright (Renato de
  Pontes Pereira, 2014) as required by the upstream license, plus
  henrytien (2026) for the independent maintenance.
- CONTRIBUTING: build/test/format expectations and naming conventions.
- CHANGELOG: Keep a Changelog format, documenting this round of work.

Author: henrytien

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project are documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+### Added
+- Optional library logger (`Logf` / `SetLogger` / `SetLogOutput`), silent by
+  default so the library never writes to stdout unasked.
+- `loader.CreateBehaviorTreeFromConfigSafe`: an error-returning loader that
+  recovers from malformed-config panics instead of crashing the process.
+- Core unit tests for composites (Sequence, Priority), the Inverter decorator,
+  and `RUNNING` tick propagation.
+- Bilingual (中文 / English) documentation site built with Docusaurus, plus a
+  "Design Notes" page covering node concepts and implementation-specific tips.
+- CI workflows: cross-platform Go build/vet/test, and automatic deployment of
+  the documentation site to GitHub Pages.
+- `LICENSE`, `CONTRIBUTING.md`, and this `CHANGELOG.md`.
+
+### Changed
+- Renamed the import alias `b3` to `bt` across the codebase to match the
+  behavior-tree naming (pure alias rename, no behavior change).
+- Standardized naming: external brand / module path is `behavior-tree`; the Go
+  package declaration is `behaviortree`.
+- Upgraded the Go directive to 1.23.
+- Rewrote the README with installation, a quick-start example, and a built-in
+  node overview; removed outdated local-editor setup steps.
+
+### Fixed
+- Corrected copy-paste panic messages in the `Limiter`, `MaxTime`, `Repeater`,
+  `RepeatUntilFailure`, and `RepeatUntilSuccess` decorators, which all named
+  the wrong decorator type.
+- Removed dead `unreachable code` after `panic` in the config package and
+  replaced the deprecated `io/ioutil` with `os`.
+- Replaced dead external links (behaviac.com, the Youdao note) with stable
+  references.
+
+## [0.2.0]
+
+Earlier history, inherited from `magicsea/behavior3go`:
+
+### Added
+- `SubTree` node support (requires the editor to export the node `category`).
+- `RandWait` action: random wait supporting `min_ms`/`max_ms`, compatible with
+  `timemini`/`timemax` and a fixed `milliseconds`.
+- `Probability` decorator: supports `probability`/`rate`/`percent` and
+  `skip_status`.
+
+[Unreleased]: https://github.com/henrytien/behavior-tree/compare/master...HEAD

CONTRIBUTING.md

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+# Contributing
+
+Thanks for your interest in improving **behavior-tree**! This project is a Go
+implementation of the [behavior3](https://github.com/behavior3) behavior tree,
+maintained independently at `github.com/henrytien/behavior-tree`.
+
+## Getting started
+
+Requires Go 1.23 or later.
+
+```bash
+git clone https://github.com/henrytien/behavior-tree
+cd behavior-tree
+go build ./...
+go test ./...
+```
+
+## Before opening a pull request
+
+Please make sure the following all pass locally:
+
+```bash
+gofmt -l .        # should print nothing
+go vet ./...      # should report nothing
+go test ./...     # should pass
+```
+
+- **Format**: code must be `gofmt`-clean.
+- **Tests**: add tests for new behavior. Core behavior tests live in
+  `loader/` (the loader package imports every node package, so trees can be
+  assembled from JSON configs in tests without import cycles).
+- **No stray output**: the library must stay silent by default. Route any
+  diagnostic output through `Logf` rather than `fmt.Println`.
+- **Backward compatibility**: avoid breaking the existing public API. Prefer
+  additive changes (for example, the error-returning `...Safe` loader sits
+  alongside the panic-based one).
+
+## Commit messages
+
+Use short, imperative, English commit subjects with a type prefix, e.g.:
+
+```
+feat: add CreateBehaviorTreeFromConfigSafe returning an error
+fix: correct copy-paste panic messages in decorators
+docs: add Design Notes page
+test: add core behavior tests for composites
+```
+
+## Naming conventions
+
+- External brand, repository, module path, docs: `behavior-tree`.
+- Go package declaration: `behaviortree` (Go package names cannot contain
+  hyphens).
+- Import alias used throughout the code and examples: `bt`.
+
+## Documentation
+
+User-facing docs live under `website/` (Docusaurus, bilingual 中文 / English).
+Chinese is the default locale; English translations live under
+`website/i18n/en/`. When you change behavior, update the matching doc page in
+both languages.
+
+## Reporting issues
+
+When filing a bug, please include the behavior tree JSON (or a minimal
+reproduction), the Go version, and what you expected versus what happened.

LICENSE

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+The MIT License (MIT)
+
+Copyright (c) 2014 Renato de Pontes Pereira
+Copyright (c) 2026 henrytien
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.