gui: add Wails v3 desktop app skeleton

- Go upgraded to 1.25.10 (required by Wails v3)
- Wails v3 installed (alpha.96)
- Frontend: Svelte+Vite scaffold in frontend/
- guimain.go: Wails GUI entry point (compiled with -tags gui)
- wails_service.go: stub service for Wails bindings
- Verstak desktop binary builds: go build -tags gui -o verstak-gui .
- CLI (./cmd/verstak/) unaffected
- Legacy HTTP GUI (internal/gui/) preserved as prototype
- Build: 24MB ELF binary with GTK4/WebKit2GTK-6

Build commands:
  CLI:  go build -o verstak ./cmd/verstak/
  GUI:  cd frontend && npm run build && go build -tags gui -o verstak-gui .

frontend/public/style.css

@@ -0,0 +1,157 @@
+:root {
+    font-family: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto",
+    "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue",
+    sans-serif;
+    font-size: 16px;
+    line-height: 24px;
+    font-weight: 400;
+    color-scheme: light dark;
+    color: rgba(255, 255, 255, 0.87);
+    background-color: rgba(27, 38, 54, 1);
+    font-synthesis: none;
+    text-rendering: optimizeLegibility;
+    -webkit-font-smoothing: antialiased;
+    -moz-osx-font-smoothing: grayscale;
+    -webkit-text-size-adjust: 100%;
+    user-select: none;
+    -webkit-user-select: none;
+    -moz-user-select: none;
+    -ms-user-select: none;
+}
+
+@font-face {
+    font-family: "Inter";
+    font-style: normal;
+    font-weight: 400;
+    src: local(""),
+    url("./Inter-Medium.ttf") format("truetype");
+}
+
+h3 {
+    font-size: 3em;
+    line-height: 1.1;
+}
+
+a {
+    font-weight: 500;
+    color: #646cff;
+    text-decoration: inherit;
+}
+
+a:hover {
+    color: #535bf2;
+}
+
+button {
+    width: 60px;
+    height: 30px;
+    line-height: 30px;
+    border-radius: 3px;
+    border: none;
+    margin: 0 0 0 20px;
+    padding: 0 8px;
+    cursor: pointer;
+}
+
+.result {
+    height: 20px;
+    line-height: 20px;
+}
+
+body {
+    margin: 0;
+    display: flex;
+    place-items: center;
+    place-content: center;
+    min-width: 320px;
+    min-height: 100vh;
+}
+
+.container {
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    justify-content: center;
+}
+
+h1 {
+    font-size: 3.2em;
+    line-height: 1.1;
+}
+
+#app {
+    max-width: 1280px;
+    margin: 0 auto;
+    padding: 2rem;
+    text-align: center;
+}
+
+.logo {
+    height: 6em;
+    padding: 1.5em;
+    will-change: filter;
+}
+
+.logo:hover {
+    filter: drop-shadow(0 0 2em #e80000aa);
+}
+
+.logo.vanilla:hover {
+    filter: drop-shadow(0 0 2em #f7df1eaa);
+}
+
+.result {
+    height: 20px;
+    line-height: 20px;
+    margin: 1.5rem auto;
+    text-align: center;
+}
+
+.footer {
+    margin-top: 1rem;
+    align-content: center;
+    text-align: center;
+}
+
+@media (prefers-color-scheme: light) {
+    :root {
+        color: #213547;
+        background-color: #ffffff;
+    }
+
+    a:hover {
+        color: #747bff;
+    }
+
+    button {
+        background-color: #f9f9f9;
+    }
+}
+
+
+.input-box .btn:hover {
+    background-image: linear-gradient(to top, #cfd9df 0%, #e2ebf0 100%);
+    color: #333333;
+}
+
+.input-box .input {
+    border: none;
+    border-radius: 3px;
+    outline: none;
+    height: 30px;
+    line-height: 30px;
+    padding: 0 10px;
+    color: black;
+    background-color: rgba(240, 240, 240, 1);
+    -webkit-font-smoothing: antialiased;
+}
+
+.input-box .input:hover {
+    border: none;
+    background-color: rgba(255, 255, 255, 1);
+}
+
+.input-box .input:focus {
+    border: none;
+    background-color: rgba(255, 255, 255, 1);
+}

frontend/public/svelte.svg

@@ -0,0 +1 @@
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