Add branding: Focus mark, wordmark, banner, social preview

- assets/branding/: icon (SVG + 512px PNG for Gitea avatar), adaptive-icon
  foreground/background layers, path-only wordmark for dark/light grounds,
  1200x300 README banner, 1280x640 social preview (SVG + PNG)
- README: banner hero
- build-status: branding decision log (includes the pending website section
  from the parallel web/ session, interleaved in the same file)

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

assets/branding/banner.svg

@@ -0,0 +1,39 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1200 300">
+  <rect width="1200" height="300" fill="#071522"/>
+  <!-- graduated rule -->
+  <path d="M 0 250 H 1200" fill="none" stroke="#0F2E3D" stroke-width="1.5"/>
+  <path d="M 30 255 H 1180" fill="none" stroke="#0F2E3D" stroke-width="9" stroke-dasharray="1.5 58.5"/>
+  <!-- glyph: focus -->
+  <g transform="translate(60,15) scale(2.8)">
+    <g fill="#1E4A5C">
+      <circle cx="24" cy="24" r="2.6"/><circle cx="48" cy="24" r="2.6"/><circle cx="72" cy="24" r="2.6"/>
+      <circle cx="24" cy="48" r="2.6"/><circle cx="72" cy="48" r="2.6"/>
+      <circle cx="24" cy="72" r="2.6"/><circle cx="48" cy="72" r="2.6"/><circle cx="72" cy="72" r="2.6"/>
+    </g>
+    <circle cx="48" cy="48" r="8" fill="none" stroke="#FFB454" stroke-opacity="0.3" stroke-width="2"/>
+    <circle cx="48" cy="48" r="4.5" fill="#FFB454"/>
+    <g fill="none" stroke="#35E0C4" stroke-width="3.5" stroke-linecap="round" stroke-linejoin="round">
+      <path d="M 33 41 V 33 H 41"/>
+      <path d="M 55 33 H 63 V 41"/>
+      <path d="M 63 55 V 63 H 55"/>
+      <path d="M 41 63 H 33 V 55"/>
+    </g>
+  </g>
+  <!-- wordmark -->
+  <g transform="translate(350,182)">
+    <g fill="none" stroke="#E8F4F2" stroke-width="11" stroke-linecap="round">
+      <path d="M 0 -24 H 48"/>
+      <path d="M 48 -24 A 24 24 0 1 0 40.97 -7.03"/>
+      <path d="M 110.97 -40.97 A 24 24 0 1 0 110.97 -7.03"/>
+      <path d="M 140 -76 V 0"/>
+      <path d="M 140 -24 A 24 24 0 0 1 188 -24 L 188 0"/>
+      <circle cx="234" cy="-24" r="24"/>
+      <path d="M 280 -76 V 0"/>
+      <circle cx="326" cy="-24" r="24" stroke="#35E0C4"/>
+      <path d="M 372 -48 H 402"/>
+      <path d="M 387 -68 V 0"/>
+    </g>
+    <circle cx="326" cy="-24" r="6.5" fill="#FFB454"/>
+  </g>
+  <text x="352" y="228" font-family="ui-monospace,'Cascadia Code','SF Mono',Menlo,Consolas,monospace" font-size="19" letter-spacing="3.5" fill="#5E8B96">measure, don't guess</text>
+</svg>