Rewrite backend in Rust, add Impressum, privacy policy and account tools

New axum server in backend/ with the same HTTP API and database as the
Python one. The pl8list session is only held in memory during the feed
crawl and logged out afterwards. Local sessions use a __Host- cookie,
30-day idle expiry and weekly token rotation; the old cookie is migrated.

The audio and image proxy only accepts known parameters, fixes the content
type, follows redirects only to pl8list's file host and caches segments and
images on disk. Strict security headers, origin checks on POST, body and
concurrency limits.

/impressum and /datenschutz are rendered from env variables. The account
menu offers data export, sign out on all devices and account deletion.
hls.js is self-hosted and artist images are proxied, so the browser only
talks to this server. The Docker image builds a static binary on scratch.

static/app.js

@@ -16,6 +16,8 @@ const filtersForm = document.getElementById("filters");
 const filtersBtn = document.getElementById("filters-btn");
 const likesPanel = document.getElementById("likes");
 const likesBtn = document.getElementById("likes-btn");
+const accountPanel = document.getElementById("account");
+const accountBtn = document.getElementById("account-btn");
 const startEl = document.getElementById("start");
 const helpEl = document.getElementById("help");
 const toastEl = document.getElementById("toast");
@@ -86,6 +88,8 @@ function showStats(s) {
 // Uploads are often titled after their file name.
 const cleanTitle = (t) => t.replace(/\.(wav|mp3|flac|aiff?|ogg|m4a)$/i, "");
 const trackUrl = (t) => `${PL8}/${t.handle}/${t.slug}`;
+// Images come through our server, so pl8list never sees the visitor's address.
+const artistImg = (t) => `/img/${encodeURIComponent(t.artist_img)}`;
 const fmtTime = (s) => `${Math.floor(s / 60)}:${String(Math.floor(s % 60)).padStart(2, "0")}`;
 
 let toastTimer = 0;
@@ -100,7 +104,7 @@ function toast(text, ms = 2200) {
 
 function buildCard(track, { liked = false } = {}) {
   const el = tpl.content.firstElementChild.cloneNode(true);
-  const img = track.artist_img ? `url("${PL8}/img/${track.artist_img}")` : "";
+  const img = track.artist_img ? `url("${artistImg(track)}")` : "";
   el.querySelector(".bg").style.backgroundImage = img;
   if (img) el.querySelector(".art").style.backgroundImage = img;
   else el.querySelector(".initial").textContent = (track.artist_name || "?")[0].toUpperCase();
@@ -377,7 +381,7 @@ const observer = new IntersectionObserver((entries) => {
 function updateMediaSession(track) {
   if (!("mediaSession" in navigator)) return;
   const artwork = [{ src: "/static/icons/icon-512.png", sizes: "512x512", type: "image/png" }];
-  if (track.artist_img) artwork.unshift({ src: `${PL8}/img/${track.artist_img}`, sizes: "512x512" });
+  if (track.artist_img) artwork.unshift({ src: artistImg(track), sizes: "512x512" });
   navigator.mediaSession.metadata = new MediaMetadata({
     title: cleanTitle(track.title),
     artist: track.artist_name,
@@ -471,7 +475,7 @@ feed.addEventListener("click", (e) => {
 
 // Panels and overlays -----------------------------------------------------
 
-const panels = [[filtersForm, filtersBtn], [likesPanel, likesBtn]];
+const panels = [[filtersForm, filtersBtn], [likesPanel, likesBtn], [accountPanel, accountBtn]];
 
 function closePanels() {
   for (const [panel, btn] of panels) {
@@ -692,15 +696,48 @@ document.getElementById("resend").addEventListener("click", () => {
 
 document.getElementById("restart").addEventListener("click", showLogin);
 
+// Account -----------------------------------------------------------------
+
+const deleteForm = document.getElementById("delete-form");
+
+accountBtn.addEventListener("click", () => {
+  if (togglePanel(accountPanel)) deleteForm.hidden = true;
+});
+
 document.getElementById("logout-btn").addEventListener("click", async () => {
   await postJSON("/auth/logout");
   location.reload();
 });
 
+document.getElementById("logout-all-btn").addEventListener("click", async () => {
+  await postJSON("/account/logout-all");
+  location.reload();
+});
+
+document.getElementById("delete-open").addEventListener("click", () => {
+  deleteForm.hidden = false;
+  deleteForm.confirm.value = "";
+  deleteForm.confirm.focus();
+});
+
+deleteForm.addEventListener("submit", async (e) => {
+  e.preventDefault();
+  try {
+    await postJSON("/account/delete", { confirm: deleteForm.confirm.value.trim() });
+    localStorage.removeItem(FILTERS_KEY);
+    localStorage.removeItem(HINT_KEY);
+    location.reload();
+  } catch (err) {
+    toast(err.message, 4000);
+  }
+});
+
 function signedIn(user) {
   loginEl.hidden = true;
   document.getElementById("bar").hidden = false;
-  document.getElementById("logout-btn").textContent = `sign out @${user.handle}`;
+  accountBtn.textContent = `@${user.handle}`;
+  document.getElementById("account-handle").textContent = `@${user.handle}`;
+  document.getElementById("delete-handle").textContent = user.handle;
   // Typing the login code counts as a user gesture, so playback may start right away.
   if (navigator.userActivation?.hasBeenActive) start();
   else if (!started) startEl.hidden = false;