add(deepseek_usage): DeepSeek API credit & balance monitor (#220)

* add(deepseek_usage): add DeepSeek usage balance monitor plugin

* add(deepseek_usage): add thumbnail.webp

* chore(deepseek_usage): update plugin id to coder/deepseek_usage

* fix(deepseek_usage): update 960x540 thumbnail, README IPC docs, and plugin.toml schema

* fix(deepseek_usage): fix panel ID, normalize ui.graph values 0-1, declare xdg-open dependency

* fix(deepseek_usage): replace thumbnail with official Noctalia generator asset

deepseek_usage/README.md

@@ -0,0 +1,43 @@
+# DeepSeek Usage Plugin for Noctalia
+
+A balance and API credit monitor for [Noctalia shell](https://noctalia.dev).
+
+## Plugin
+
+Plugin ID: `coder/deepseek_usage`
+
+Widget(s):
+- `bar` — bar widget entry.
+
+Panel(s):
+- `panel` — panel entry.
+
+## Requirements
+
+- `xdg-open` — used by the top-up button to open platform.deepseek.com/top_up in the default browser.
+
+## External dependencies
+
+- `xdg-open`
+
+## Usage
+
+Widget
+- Add the `bar` widget to your bar to display usage.
+
+Panel
+- Toggle the plugin panel with the following IPC command:
+  `noctalia msg panel-toggle coder/deepseek_usage:panel`
+
+## Features
+- **Bar Widget**: Shows live balance directly on your Noctalia bar.
+- **Low Balance Warning**: Visual indicator and desktop notifications when credits drop below your set threshold.
+- **Interactive Panel**: Displays account wallet summary, local trend graph, and quick top-up action.
+- **One-Click Top-Up**: "Add Credits" button opens `platform.deepseek.com/top_up` directly in your browser.
+
+## Settings
+Configure the update interval and API key in Noctalia plugin settings.
+
+- **DeepSeek API Key**: Create an API key at [platform.deepseek.com/api_keys](https://platform.deepseek.com/api_keys) and enter it in plugin settings.
+- **Refresh Interval**: Default is 15 minutes.
+- **Low Balance Warning**: Default threshold is 2.00.