docs: add project logo and embed in README

Geometric house icon on blue gradient rounded square (SVG).
Replaces shields.io badge placeholder in README hero section.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -1,7 +1,5 @@
 <p align="center">
-  <!-- Replace with your logo when ready: recommended 120–160px, SVG or PNG, transparent background -->
-  <!-- <img src="docs/logo.svg" alt="Oikos" width="140"> -->
-  <img src="https://img.shields.io/badge/%F0%9F%8F%A0-Oikos-007AFF?style=for-the-badge&labelColor=F5F5F7" alt="Oikos" height="48">
+  <img src="docs/logo.svg" alt="Oikos" width="140">
 </p>
 
 <h1 align="center">Oikos</h1>

docs/logo.svg

@@ -0,0 +1,13 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 160 160" fill="none">
+  <defs>
+    <linearGradient id="bg" x1="0" y1="0" x2="160" y2="160" gradientUnits="userSpaceOnUse">
+      <stop offset="0%" stop-color="#0A84FF"/>
+      <stop offset="100%" stop-color="#006AE0"/>
+    </linearGradient>
+  </defs>
+  <rect width="160" height="160" rx="36" fill="url(#bg)"/>
+  <!-- House body + roof -->
+  <path d="M80 36L36 72V120C36 122.2 37.8 124 40 124H68V96H92V124H120C122.2 124 124 122.2 124 120V72L80 36Z" fill="white"/>
+  <!-- Chimney -->
+  <rect x="100" y="46" width="12" height="22" rx="2" fill="white"/>
+</svg>