Docs: replace README hero image with new HARDAX overview, host in-repo (#25)

- Remove reference to https://raw.githubusercontent.com/V33RU/my-slides/refs/heads/main/images/report.png (separate repo, external dependency).
- Add .github/assets/hardax-overview.png (1.8 MB PNG, 1536x1024). The new image shows the HARDAX logo, dashboard mockup, mobile preview, feature list (System Configuration, Data Protection, Permission Management, IoT & Hardware Security, etc.), and the "Designed for" audience grid (Security Researchers, IoT Security Teams, POS Security Auditors, Enterprise Security, Developers).
- README points at the new image via its raw GitHub URL so it renders correctly on both GitHub and the PyPI project page (PyPI renders README from the wheel which does not contain .github/, so relative paths break there).

Pure documentation change. No code, JSON, or workflow files touched. The image is not included in the pip wheel (only hardax/ package data is), so installed-package size is unchanged.

Author: V33RU

.github/assets/hardax-overview.png

@@ -28,7 +28,7 @@
 <p align="center">
 </p>
 
-![](https://raw.githubusercontent.com/V33RU/my-slides/refs/heads/main/images/report.png)
+![HARDAX overview: Android security configuration auditor](https://raw.githubusercontent.com/V33RU/hardax/main/.github/assets/hardax-overview.png)
 
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