Polish store and v2rayA app for release

- Redesign store README as a minimal storefront

- Refine app README and remove technical clutter

- Update Sphera icon with refined vector styling

- Use original v2rayA app icon

- Use raw GitHub URL for v2rayA icon per Umbrel Community Store spec

- Add custom v2rayA image build for UmbrelOS nf_tables iptables

README.md

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+<p align="center">
+  <img src="sphera-icon.svg" width="128" height="128" alt="Sphera">
+</p>
+
+<h1 align="center">Sphera</h1>
+
+<p align="center">
+  <strong>Community App Store for UmbrelOS</strong>
+</p>
+
+<p align="center">
+  <a href="https://umbrel.com"><img src="https://img.shields.io/badge/Umbrel-Community%20Store-5F8DD3?style=for-the-badge&logo=umbrel&logoColor=white" alt="Umbrel Community Store"></a>
+  <img src="https://img.shields.io/badge/apps-1-blue?style=for-the-badge" alt="1 app">
+</p>
+
+<p align="center">
+  Curated tools that extend what your personal server can do.
+</p>
+
+---
+
+## Install
+
+In UmbrelOS go to **App Store → Community App Stores → Add** and paste:
+
+```
+https://github.com/cheviiot/Sphera
+```
+
+---
+
+## Apps
+
+| | Name | ID | Description |
+|:---:|---|---|---|
+| <img src="sphera-v2raya/icon.png" width="40" height="40" alt="v2rayA"> | **v2rayA** | `sphera-v2raya` | Web GUI client for V2Ray / Xray. Transparent proxy via host networking. |
+
+---
+
+<p align="center">
+  <sub>Made for the Umbrel community.</sub>
+</p>