Add README and proper favicon/PWA icon set

README covers what alembic does, prerequisites, a full deploy quickstart,
credential setup, and a page-by-page usage tour, written for someone
running Docker but not necessarily comfortable coding or sysadmin work.

Favicon/icons were prepared in a separate theme scratch dir but never
wired in; moved them into app/static and pointed base.html at the full
icon set (SVG, PNG fallbacks, apple-touch-icon, manifest) instead of the
single inline data-URI SVG it had before.

app/static/icon.svg

@@ -0,0 +1,35 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="512" height="512" viewBox="0 0 512 512">
+  <defs>
+    <linearGradient id="bgGrad" x1="0" y1="0" x2="0" y2="1">
+      <stop offset="0%" stop-color="#14151f"></stop>
+      <stop offset="100%" stop-color="#05050a"></stop>
+    </linearGradient>
+    <radialGradient id="glow" cx="50%" cy="46%" r="55%">
+      <stop offset="0%" stop-color="#a78bfa" stop-opacity="0.55"></stop>
+      <stop offset="55%" stop-color="#67e8f9" stop-opacity="0.18"></stop>
+      <stop offset="100%" stop-color="#67e8f9" stop-opacity="0"></stop>
+    </radialGradient>
+    <linearGradient id="flaskGrad" x1="146" y1="113" x2="301" y2="377" gradientUnits="userSpaceOnUse">
+      <stop offset="0%" stop-color="#7dd3fc"></stop>
+      <stop offset="50%" stop-color="#a78bfa"></stop>
+      <stop offset="100%" stop-color="#f9a8d4"></stop>
+    </linearGradient>
+    <filter id="blur" x="-60%" y="-60%" width="220%" height="220%">
+      <feGaussianBlur stdDeviation="34"></feGaussianBlur>
+    </filter>
+    <path id="star" d="M12 0c.6 5.7 1.8 8.6 4.2 10.6 2.4 2 5.3 2.6 7.8 3.4-2.5.8-5.4 1.4-7.8 3.4-2.4 2-3.6 4.9-4.2 10.6-.6-5.7-1.8-8.6-4.2-10.6C5.4 15.4 2.5 14.8 0 14c2.5-.8 5.4-1.4 7.8-3.4C10.2 8.6 11.4 5.7 12 0Z"></path>
+  </defs>
+
+  <rect x="0" y="0" width="512" height="512" rx="112" fill="url(#bgGrad)"></rect>
+  <rect x="1.5" y="1.5" width="509" height="509" rx="110.5" fill="none" stroke="#ffffff" stroke-opacity="0.06"></rect>
+
+  <circle cx="256" cy="236" r="150" fill="url(#glow)" filter="url(#blur)"></circle>
+
+  <use href="#star" x="118" y="108" width="30" height="30" fill="#e9e6ff" opacity="0.55"></use>
+  <use href="#star" x="366" y="352" width="22" height="22" fill="#bff3ff" opacity="0.5"></use>
+
+  <g>
+    <path d="M211 113.5h90v78l64.5 129a39 39 0 0 1 -34.95 56.4H181.45A39 39 0 0 1 146.5 320.5L211 191.5V113.5z" fill="url(#flaskGrad)"></path>
+    <path d="M211 113.5h90M199 205h114" stroke="#08090d" stroke-width="13.5" stroke-linecap="round" opacity="0.35"></path>
+  </g>
+</svg>

app/static/site.webmanifest

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+{
+  "name": "Alembic",
+  "short_name": "Alembic",
+  "description": "Playlist ingestion, tagging, dedupe, and library tools for Alembic.",
+  "start_url": "/",
+  "display": "standalone",
+  "background_color": "#08090d",
+  "theme_color": "#08090d",
+  "icons": [
+    { "src": "/static/icon-192.png", "sizes": "192x192", "type": "image/png" },
+    { "src": "/static/icon-512.png", "sizes": "512x512", "type": "image/png" }
+  ]
+}