feat(ui): drag-drop capture onto the main panel

Drops into #main POST /api/capture/upload one file at a time, with
space_id pre-filled from localStorage.last_space_id (set whenever the
space view renders).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

public/app.js

@@ -9,6 +9,7 @@ import { renderTopbar } from './components/topbar.js';
 import { renderRightrail } from './components/rightrail.js';
 import { emit } from './state.js';
 import { el, mount } from './dom.js';
+import { attachDropzone } from './components/dropzone.js';
 
 const VIEWS = {
   home:            () => import('./views/home.js'),
@@ -56,6 +57,7 @@ async function init() {
   renderTopbar(document.getElementById('topbar'));
   renderSidebar(document.getElementById('sidebar'));
   renderRightrail(document.getElementById('rightrail'));
+  attachDropzone(document.getElementById('main'));
   route(renderView);
   pollPending();
   setInterval(pollPending, 15000);

public/components/dropzone.js

@@ -0,0 +1,42 @@
+// Drag-drop wrapper for /api/capture/upload. Pre-fills space_id from
+// localStorage.last_space_id (set when the space view renders).
+
+export function attachDropzone(target) {
+  function highlight(on) {
+    target.style.outline = on ? '2px dashed var(--accent)' : '';
+    target.style.outlineOffset = on ? '-6px' : '';
+  }
+  let counter = 0;   // dragenter/leave on children would otherwise toggle
+  target.addEventListener('dragenter', e => { e.preventDefault(); counter++; if (counter === 1) highlight(true); });
+  target.addEventListener('dragleave', () => { counter = Math.max(0, counter - 1); if (counter === 0) highlight(false); });
+  target.addEventListener('dragover', e => { e.preventDefault(); });
+  target.addEventListener('drop', async e => {
+    e.preventDefault();
+    counter = 0;
+    highlight(false);
+    const files = [...(e.dataTransfer?.files || [])];
+    if (!files.length) return;
+    const space_id = localStorage.getItem('last_space_id');
+    if (!space_id) {
+      alert('Open a space first so we know where to drop these.');
+      return;
+    }
+    const token = localStorage.getItem('void_token') || '';
+    let ok = 0, fail = 0;
+    for (const f of files) {
+      const fd = new FormData();
+      fd.append('file', f);
+      fd.append('space_id', space_id);
+      try {
+        const res = await fetch('/api/capture/upload', {
+          method: 'POST',
+          headers: { Authorization: 'Bearer ' + token },
+          body: fd
+        });
+        if (res.ok) ok++; else fail++;
+      } catch { fail++; }
+    }
+    const msg = `${ok} file${ok === 1 ? '' : 's'} queued` + (fail ? ` (${fail} failed)` : '');
+    console.log(msg);
+  });
+}

public/views/space.js

@@ -33,6 +33,7 @@ export async function render(main, ctx) {
     el('p', { class: 'view-sub muted' }, 'Loading …')
   );
 
+  localStorage.setItem('last_space_id', id);
   let space;
   try { space = await api.get('/api/spaces/' + id); }
   catch (e) {