docs: GPLv3 LICENSE + NOTICE + License-Hinweise in README EN/DE

NOTICE.md

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+# NOTICE
+
+This repository contains code licensed under the **GNU General Public License
+v3.0** (see [LICENSE](LICENSE)) and material that is **not** covered by that
+license. Read this file before forking, distributing, or building from source.
+
+## What is GPLv3-licensed
+
+The original work in this repository:
+
+- `bridge/` — Bridge daemon, MQTT client, web UI, configuration loader,
+  protocol implementation
+- `tools/` — `extract_credentials`, `fetch_credentials` utilities
+- `_archive/tools/kx_printer_emulator.py` — printer emulator
+- `Dockerfile`, `docker-compose.yml`, `release.sh`, build scripts
+- Documentation files (`README*`, `CHANGELOG*`, `_archive/RE/06_docs/*`)
+- `kobra_x_orcaslicer_preset.zip` — slicer profile derived from public OrcaSlicer
+  presets, adapted for the Kobra X
+
+You are free to use, modify and redistribute this code under the terms of
+GPLv3 — including for commercial purposes — provided downstream forks remain
+under GPLv3 and source is made available to recipients.
+
+## What is **not** GPLv3-licensed
+
+The following items are **third-party material**, included here only for
+**interoperability purposes** as permitted under §69e UrhG (German Copyright
+Act; equivalent: EU Software Directive Art. 6, US fair-use for reverse
+engineering for interoperability):
+
+- **`bridge/anycubic_slicer.crt`** and **`bridge/anycubic_slicer.key`** —
+  TLS client certificate and private key extracted from Anycubic Slicer Next
+  binaries. Copyright remains with Anycubic / their respective authors.
+  Included solely to enable the bridge to authenticate against the LAN MQTT
+  broker that runs on a Kobra X printer the end-user already owns. No
+  ownership claim is made.
+
+- **MQTT protocol structures, payload formats and signature algorithms** —
+  reverse-engineered from `Workbench.dll` / `cloud_mqtt.dll` of the Anycubic
+  Slicer Next application. The protocol itself is documented in
+  `_archive/RE/06_docs/` for transparency. Any reproduction of code or
+  protocol details serves interoperability only.
+
+- **AMS material naming, slot numbering, GCode markers (`EXCLUDE_OBJECT_*`)**
+  — follow conventions established by Anycubic and the wider Klipper
+  ecosystem; usage here is purely interoperability-driven.
+
+## What this means for forks
+
+If you fork KX-Bridge:
+
+1. **You must keep this `NOTICE.md` and `LICENSE` file** in your fork.
+2. Your modifications and additions to the bridge code, UI, tools and docs
+   inherit GPLv3 — they must be made available under the same license if you
+   distribute them.
+3. The third-party material listed above is **not** something you can
+   relicense; it stays under the original (implicit) rights of its owners.
+4. Removing the certificates and rebuilding them from your own Anycubic
+   Slicer installation is the safest path for redistribution if you are
+   unsure about the §69e situation in your jurisdiction.
+
+## Disclaimer
+
+This project is independent, non-commercial reverse-engineering work. It is
+**not** affiliated with, endorsed by, or supported by Anycubic Technology
+Co., Ltd. or any of their subsidiaries.
+
+All trademarks are property of their respective owners.