Add campaign layer, GPU model caching, file browser cleanup

- Campaigns: new table, CRUD API, React context + provider
- Sessions: scoped to campaigns, paths under campaigns/{id}/
- File browser: scoped per campaign, removed copy/paste/autoPlay
- Sidebar: campaign selector dropdown at top
- Transcribe: GPU model cached/released via job counter
- Jobs: status text updates dynamically in real-time
- Auto-redirect: blocked when summarize job is active

frontend/src/pages/Campaigns.tsx

@@ -0,0 +1,120 @@
+import { useEffect, useState } from 'react';
+import { useNavigate } from 'react-router-dom';
+import { campaignApi, type Campaign } from '../api';
+import { useCampaign } from '../contexts/CampaignContext';
+
+export default function Campaigns() {
+  const [campaigns, setCampaigns] = useState<Campaign[]>([]);
+  const [name, setName] = useState('');
+  const [editingId, setEditingId] = useState<string | null>(null);
+  const [editName, setEditName] = useState('');
+  const nav = useNavigate();
+  const { setCampaign, refreshCampaigns } = useCampaign();
+
+  const load = async () => {
+    const list = await campaignApi.list();
+    setCampaigns(list);
+  };
+
+  useEffect(() => { load(); }, []);
+
+  const create = async () => {
+    if (!name.trim()) return;
+    const c = await campaignApi.create(name.trim());
+    setName('');
+    await load();
+    await refreshCampaigns();
+    setCampaign(c);
+    nav('/');
+  };
+
+  const startEdit = (c: Campaign) => {
+    setEditingId(c.id);
+    setEditName(c.name);
+  };
+
+  const saveEdit = async (id: string) => {
+    if (!editName.trim()) return;
+    await campaignApi.update(id, { name: editName.trim() });
+    setEditingId(null);
+    await load();
+    await refreshCampaigns();
+  };
+
+  const deleteCampaign = async (id: string) => {
+    if (!confirm('Delete this campaign? Sessions will be unlinked (notes/history preserved).')) return;
+    await campaignApi.delete(id);
+    await load();
+    await refreshCampaigns();
+  };
+
+  const select = (c: Campaign) => {
+    setCampaign(c);
+    nav('/');
+  };
+
+  return (
+    <div className="max-w-3xl mx-auto py-16 px-4">
+      <div className="eyebrow mb-2">Nat20 Notes</div>
+      <h1 className="font-display text-4xl mb-8">Campaigns</h1>
+
+      <div className="card p-6 mb-8">
+        <h2 className="font-display text-xl mb-4">New campaign</h2>
+        <div className="flex gap-3">
+          <input
+            className="input flex-1"
+            placeholder="Campaign name"
+            value={name}
+            onChange={(e) => setName(e.target.value)}
+            onKeyDown={(e) => e.key === 'Enter' && create()}
+          />
+          <button className="btn-primary" disabled={!name.trim()} onClick={create}>
+            Create
+          </button>
+        </div>
+      </div>
+
+      <div className="space-y-3">
+        {campaigns.length === 0 && (
+          <p className="text-ink/40">No campaigns yet — create one above.</p>
+        )}
+        {campaigns.map((c) => (
+          <div key={c.id} className="card p-4 flex items-center justify-between hover:border-brass/40 border border-transparent">
+            <div className="flex-1 min-w-0 cursor-pointer" onClick={() => select(c)}>
+              {editingId === c.id ? (
+                <input
+                  className="input w-full"
+                  value={editName}
+                  onChange={(e) => setEditName(e.target.value)}
+                  onKeyDown={(e) => {
+                    if (e.key === 'Enter') saveEdit(c.id);
+                    if (e.key === 'Escape') setEditingId(null);
+                  }}
+                  onBlur={() => saveEdit(c.id)}
+                  autoFocus
+                  onClick={(e) => e.stopPropagation()}
+                />
+              ) : (
+                <>
+                  <div className="font-medium">{c.name}</div>
+                  <div className="text-xs text-ink/40 mt-0.5">
+                    {c.session_count} session{c.session_count !== 1 ? 's' : ''}
+                    {c.description && ` \u00B7 ${c.description}`}
+                  </div>
+                </>
+              )}
+            </div>
+            <div className="flex gap-2 ml-4 shrink-0">
+              <button className="btn-secondary text-xs px-2 py-1" onClick={(e) => { e.stopPropagation(); startEdit(c); }}>
+                Rename
+              </button>
+              <button className="btn-secondary text-xs px-2 py-1 text-rose-400" onClick={(e) => { e.stopPropagation(); deleteCampaign(c.id); }}>
+                Delete
+              </button>
+            </div>
+          </div>
+        ))}
+      </div>
+    </div>
+  );
+}