docs: add project logo (light + dark) to README

Drop-in <picture> element with prefers-color-scheme switching so the
dark variant renders on GitHub's dark theme and the light variant on
the light theme. Same aria-label + title on both SVGs so screen
readers get a consistent description.

H1 retained below the image so SEO + accessibility signals aren't
dependent on SVG text indexing.

Signed-off-by: Tomáš Filip <tomasfilip124@gmail.com>

Author: tomasfil

README.md

@@ -1,3 +1,11 @@
+<p align="center">
+  <picture>
+    <source media="(prefers-color-scheme: dark)" srcset="assets/logo-dark.svg">
+    <source media="(prefers-color-scheme: light)" srcset="assets/logo-light.svg">
+    <img alt="BlazeDex — Blazor/Razor-aware MCP server for .NET 10" src="assets/logo-light.svg" width="500">
+  </picture>
+</p>
+
 # BlazeDex — Blazor MCP Server
 
 [![License: Elastic-2.0](https://img.shields.io/badge/License-Elastic--2.0-blue.svg)](LICENSE)