Fix the logo's pop-in with a traced vector logo

The logo was an 880 KB SVG wrapping a 1254px PNG, downloaded again on
every page load. Keep that PNG as the master (artwork/logo.png) and have
scripts/logo.py trace it with potrace into a 6 KB logo.svg (favicon,
README) and logo.js, which brand.js draws inline in the header and on the
login page so the logo arrives with the page. Remove the unused
logo-white.svg.

Static files now carry content ETags, so reloads get 304s instead of
downloading the UI again.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/static/assets/app.js

@@ -1,6 +1,6 @@
 // Jarl web UI: router, layout and login.
 import { h, mount, toast, errorBox, plural } from "./ui.js";
-import { wordmark } from "./brand.js";
+import { wordmark, logo } from "./brand.js";
 import { api, get, state, loadDraft, onChange, setUnauthorizedHandler, setImmediate } from "./api.js";
 import * as dashboard from "./pages/dashboard.js";
 import * as zones from "./pages/zones.js";
@@ -75,7 +75,7 @@ function renderLogin(message) {
     }
   } }, user, pass, h("button", { class: "primary", type: "submit" }, "Log in"), err);
   mount(app, h("div", { class: "login panel" },
-    h("img", { class: "login-logo", src: "/assets/logo.svg", alt: "", width: 104, height: 104 }),
+    logo(104, "login-logo"),
     h("h1", null, wordmark()),
     h("div", { class: "tag" }, "Rule your DNS holds"),
     message ? h("div", { class: "msg warn" }, message) : null,
@@ -92,7 +92,7 @@ function layout() {
   const me = state.me;
   const header = h("header", { class: "top" },
     h("a", { class: "brand", href: "#/", title: "Dashboard" },
-      h("img", { src: "/assets/logo.svg", alt: "", width: 30, height: 30 }),
+      logo(30),
       h("span", { class: "brand-name" }, "Jarl"),
       h("span", { class: "brand-version" }, me.version)),
     navEl,