docs: README, license, and store thumbnail

LICENSE

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+MIT License
+
+Copyright (c) 2026 loki
+
+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.

README.md

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+# Headset Control
+
+Monitor and control [HeadsetControl](https://github.com/Sapd/HeadsetControl)-compatible gaming headsets
+from the Noctalia shell: battery in the bar, a sidetone toggle in the control center, and a full
+control panel for sidetone, equalizer presets, auto-off, noise filter, voice prompts and the volume limiter.
+
+Requires `headsetcontrol` (install via your package manager, e.g. `pacman -S headsetcontrol`).
+
+## Install
+
+```
+mkdir -p ~/.local/share/noctalia/plugins
+ln -s /path/to/this/repo/headsetcontrol ~/.local/share/noctalia/plugins/headsetcontrol
+noctalia msg plugins enable loki/headsetcontrol
+```
+
+## Usage
+
+- **Bar widget:** shows battery level. Scroll to adjust sidetone, click to open the control panel.
+- **Control center tile:** toggles sidetone on/off.
+- **Control panel:** full device controls. Controls appear only for capabilities the headset reports.
+
+## Settings
+
+| Setting | Default | Meaning |
+|---|---|---|
+| Poll interval | 60 s | How often status is refreshed |
+| Low battery threshold | 20 % | Warn below this level |
+| Default sidetone | 64 | Level used before any manual adjustment |
+| Device (VID:PID) | *(auto)* | Force a device, e.g. `3329:4b19` |
+| Mock device | off | Simulate a headset for development without hardware |
+
+## Development
+
+Edits to `.luau` files hot-reload. Trigger a manual refresh with:
+
+```
+noctalia msg plugin loki/headsetcontrol:headset all refresh
+```
+
+## License
+
+MIT