Rebrand to mtgc: pirate-ship logo, lowercase app name, mtgc binary

- New logomark: an original pirate-ship silhouette (hull, twin billowing
  sails, swallow-tail pennant) in the terracotta brand gradient on a dark
  square — a nod to the MTG card "Pirate Ship", not a reproduction of its
  art. Source at src-tauri/icons/logo-source.svg; regenerate the full
  platform icon set (desktop/Windows Store/iOS/Android) with
  `cargo tauri icon src-tauri/icons/logo-source.svg`.
- Apply it in-app via a new inline ShipLogo component (App.tsx), replacing
  the old "M" sidebar mark and "✦" empty-state mark with dark rounded
  squares containing the ship glyph.
- Rename the app to lowercase "mtgc" everywhere: window title and
  productName (tauri.conf.json), <title> (index.html), sidebar brand text,
  empty-state heading.
- Rename the Tauri package/binary mtgc-app -> mtgc (and its lib crate
  mtgc_app_lib -> mtgc_lib), so `cargo tauri build` now produces
  target/release/mtgc; updated main.rs and every README reference.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/App.tsx

@@ -45,6 +45,32 @@ const ICON_DOWNLOAD = svg(
   16,
 );
 
+/**
+ * mtgc's logomark: an original pirate-ship silhouette in the terracotta brand
+ * color (a nod to the MTG card "Pirate Ship", not a reproduction of its art).
+ * `gradientId` must be unique per instance rendered on the page at once.
+ */
+function ShipLogo({ size = 24, gradientId }: { size?: number; gradientId: string }) {
+  return (
+    <svg viewBox="0 0 200 200" width={size} height={size}>
+      <defs>
+        <linearGradient id={gradientId} x1="0" y1="0" x2="0" y2="1">
+          <stop offset="0" stopColor="var(--accent-hover)" />
+          <stop offset="1" stopColor="var(--accent-active)" />
+        </linearGradient>
+      </defs>
+      <g fill={`url(#${gradientId})`}>
+        <path d="M21,137 L179,137 L159,176 Q100,193 41,176 Z" />
+        <rect x="21" y="133" width="158" height="6" rx="3" />
+        <rect x="95" y="7" width="10" height="127" />
+        <path d="M100,32 C73,40 56,65 59,94 C60,103 71,110 87,113 L100,113 Z" />
+        <path d="M100,14 C147,26 168,73 160,114 C158,127 140,137 119,140 L100,140 Z" />
+        <path d="M100,7 L126,13 L109,18 L126,23 L100,30 Z" />
+      </g>
+    </svg>
+  );
+}
+
 const NAV: { id: Tab; label: string; icon: ReactNode }[] = [
   { id: "add", label: "Add Cards", icon: svg(<path d="M12 5v14M5 12h14" />) },
   {
@@ -223,8 +249,10 @@ export default function App() {
       <div className="app">
         <nav className="nav-rail">
           <div className="brand">
-            <span className="brand-mark">M</span>
-            <span className="brand-text">MTG Library</span>
+            <span className="brand-mark">
+              <ShipLogo size={20} gradientId="brand-ship-grad" />
+            </span>
+            <span className="brand-text">mtgc</span>
           </div>
 
           <div className="nav-items">
@@ -373,8 +401,10 @@ export default function App() {
           <div className="content">
             {!ready ? (
               <div className="empty-state">
-                <div className="empty-mark">✦</div>
-                <h2>Welcome to your MTG library</h2>
+                <div className="empty-mark">
+                  <ShipLogo size={40} gradientId="empty-ship-grad" />
+                </div>
+                <h2>Welcome to mtgc</h2>
                 <p className="hint">
                   No card database yet. Click <strong>Download card data</strong> to fetch
                   the latest cards from Scryfall (a few hundred MB, about a minute). The

src/styles.css

@@ -232,10 +232,7 @@ select option {
   width: 34px;
   height: 34px;
   border-radius: 10px;
-  background: linear-gradient(150deg, var(--accent-hover), var(--accent-active));
-  color: #fff;
-  font-weight: 800;
-  font-size: 19px;
+  background: linear-gradient(150deg, var(--bg-elev), var(--bg-rail));
   display: flex;
   align-items: center;
   justify-content: center;
@@ -543,15 +540,13 @@ select option {
   gap: 14px;
 }
 .empty-mark {
-  width: 72px;
-  height: 72px;
-  border-radius: 20px;
+  width: 88px;
+  height: 88px;
+  border-radius: 22px;
   display: flex;
   align-items: center;
   justify-content: center;
-  font-size: 36px;
-  color: #fff;
-  background: linear-gradient(150deg, var(--accent-hover), var(--accent-active));
+  background: linear-gradient(150deg, var(--bg-elev), var(--bg-rail));
   box-shadow: 0 10px 30px var(--accent-glow);
 }
 .empty-state h2 {