feat(auth): support API tokens and bearer token authentication

- Add backend services to create, list, and delete API tokens.
- Implement Bearer token authentication to resolve tokens to users.
- Register HTTP routes for managing user tokens under `/account/tokens`.
- Add tests to verify that uploads with valid Bearer tokens associate the upload with the correct user, while invalid tokens fall back to anonymous uploads.

backend/static/css/app.css

@@ -1818,3 +1818,63 @@ pre code {
 .storage-new-card .storage-card-body {
   border-top: none;
 }
+
+/* ── Access tokens ───────────────────────────────────────────────────────── */
+
+.token-create-form {
+  display: flex;
+  align-items: end;
+  gap: 0.65rem;
+  flex-wrap: wrap;
+  margin-bottom: 1rem;
+}
+
+.token-create-form label {
+  display: grid;
+  gap: 0.35rem;
+  color: var(--muted-foreground);
+  font-size: 0.82rem;
+  flex: 1;
+  min-width: 14rem;
+}
+
+.token-reveal {
+  margin-bottom: 1rem;
+  padding: 0.9rem 1rem;
+  border: 1px solid rgba(134, 239, 172, 0.3);
+  border-radius: var(--radius);
+  background: rgba(134, 239, 172, 0.08);
+}
+
+.token-reveal-title {
+  margin: 0 0 0.6rem;
+  font-size: 0.85rem;
+  font-weight: 650;
+  color: #86efac;
+}
+
+.token-reveal-row {
+  display: flex;
+  align-items: center;
+  gap: 0.5rem;
+}
+
+.token-reveal-value {
+  flex: 1;
+  min-width: 0;
+  padding: 0.5rem 0.65rem;
+  border: 1px solid var(--border);
+  border-radius: calc(var(--radius) - 0.125rem);
+  background: var(--background);
+  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, monospace;
+  font-size: 0.82rem;
+  word-break: break-all;
+}
+
+.token-reveal .muted-copy {
+  margin: 0.6rem 0 0;
+}
+
+.token-reveal .muted-copy code {
+  word-break: break-all;
+}