news-digest: real article summaries + per-desk collapse

Two upgrades to make the digest actually readable:

1) Article-grounded 2-3 sentence summaries (everywhere)

   The old prompt got just the title + miniflux's content excerpt,
   which for HN/Lobsters/wire feeds is barely more than the title
   itself — so summaries paraphrased the title and added nothing.

   Now every URL gets fetched and main-content-extracted via
   trafilatura on a parallel pre-pass (10 workers, ~15s for ~50
   URLs). Extracted text caches to /output/.article-cache.json with
   a 7-day TTL so repeat runs in the same window don't re-pull.

   Headlines also get summarized now — one batched LLM call per
   category (world / local). Rendered as a paragraph below the
   title with source + time on the right rail.

   Prompt rewrites tell the model to pull names/numbers/places
   from the body and explicitly forbid restating the title.
   Result: real specifics ("71% saw no pay increase globally",
   "third time in less than two weeks", "Islamabad and Moscow
   intermediaries") instead of title paraphrase.

2) Per-desk collapse buttons

   Chevron next to .desk-count toggles a .is-collapsed class.
   Collapsed state is per-device (localStorage by section id) since
   collapse is a viewing preference, not content state.

stacks/news-digest/templates/app.js

@@ -201,6 +201,38 @@
     });
   }
 
+  /* ── desk collapse (per-device, localStorage) ───────────────────── */
+  // Stored as a JSON object {deskId: true} of collapsed desks. Per
+  // device by design — collapse is a viewing preference, not content
+  // state, so no server roundtrip.
+  const COLLAPSE_KEY = "digest:collapsed-desks";
+  function readCollapsed() {
+    try { return JSON.parse(localStorage.getItem(COLLAPSE_KEY) || "{}"); }
+    catch (_) { return {}; }
+  }
+  function writeCollapsed(obj) {
+    try { localStorage.setItem(COLLAPSE_KEY, JSON.stringify(obj)); } catch (_) {}
+  }
+  function applyCollapseState() {
+    const state = readCollapsed();
+    document.querySelectorAll(".desk[id]").forEach((desk) => {
+      desk.classList.toggle("is-collapsed", !!state[desk.id]);
+    });
+  }
+  applyCollapseState();
+  document.addEventListener("click", (ev) => {
+    const btn = ev.target.closest(".desk-collapse");
+    if (!btn) return;
+    const desk = btn.closest(".desk[id]");
+    if (!desk) return;
+    ev.preventDefault();
+    desk.classList.toggle("is-collapsed");
+    const state = readCollapsed();
+    if (desk.classList.contains("is-collapsed")) state[desk.id] = true;
+    else delete state[desk.id];
+    writeCollapsed(state);
+  });
+
   /* ── initial paint ──────────────────────────────────────────────── */
 
   apiGetHidden().then((hidden) => {