fix(audit-g5d): surface ErrorType taxonomy on FailingSourcesCard

Alembic 0032 adds Source.error_type (varchar(32), indexed).
_update_source_health stamps it alongside last_error on status='error'
and clears it on 'ok'. SourceRecord/to_dict exposes it.

FailingSourcesCard renders a colored chip next to the consecutive-
failures count, with a tooltip explaining the suggested operator
action. Color reflects intent:
  - warning (yellow) — operator action needed (auth_error)
  - info (blue)      — backend-paced (rate_limited / timeout /
                       network_error / partial / tier_limited)
  - error (red)      — likely terminal without intervention
                       (not_found / access_denied / validation_failed /
                        unsupported_url / http_error / unknown_error)

Audit 2026-06-02: the backend computed 13 ErrorType categories but
only the free-text last_error reached the operator. Bulk-triage by
class ("all auth_error → rotate cookies", "12 rate_limited → just
wait") required opening Logs per row.

frontend/src/components/subscriptions/FailingSourcesCard.vue

@@ -25,6 +25,15 @@
           <v-chip size="x-small" color="error" variant="flat" label class="fc-fail__count">
             {{ s.consecutive_failures }}× failed
           </v-chip>
+          <v-chip
+            v-if="s.error_type"
+            size="x-small" variant="outlined" label
+            :color="errorTypeColor(s.error_type)"
+            class="fc-fail__class"
+            :title="errorTypeHint(s.error_type)"
+          >
+            {{ s.error_type }}
+          </v-chip>
           <span class="fc-fail__err" :title="s.last_error || ''">
             {{ s.last_error || 'no error message recorded' }}
           </span>
@@ -66,6 +75,42 @@ const open = ref(true)
 // Per-row loading flag so the spinner lives on the row whose Logs
 // button was clicked, not on every row.
 const logLoadingIds = ref(new Set())
+
+// Audit 2026-06-02: surface the ErrorType taxonomy as a colored chip
+// next to the consecutive-failures count so operators can bulk-triage
+// by error class. Color reflects "what to do next":
+//   warning (yellow) — auth/cookie issue: operator should rotate
+//   info (blue)      — backend-paced (cooldown / rate limit / timeout)
+//   error (red)      — likely terminal without operator intervention
+const ERROR_TYPE_COLOR = {
+  auth_error: 'warning',
+  rate_limited: 'info',
+  timeout: 'info',
+  network_error: 'info',
+  not_found: 'error',
+  access_denied: 'error',
+  validation_failed: 'error',
+  unsupported_url: 'error',
+  http_error: 'error',
+  unknown_error: 'error',
+  partial: 'info',
+  tier_limited: 'info',
+  no_new_content: 'info',
+}
+const ERROR_TYPE_HINT = {
+  auth_error: 'Cookies likely expired — re-upload in Credentials.',
+  rate_limited: 'Platform-wide cooldown active. Will retry after it expires.',
+  timeout: 'Subprocess exceeded its time budget. Often retries cleanly.',
+  network_error: 'Transient network issue. Will retry on next tick.',
+  not_found: 'URL 404 — creator may have renamed or deleted.',
+  access_denied: 'Subscription tier may not grant this content.',
+  validation_failed: 'Downloaded files were quarantined by the validator.',
+  http_error: 'Generic HTTP error — see Logs.',
+  unsupported_url: 'gallery-dl does not support this URL pattern.',
+  unknown_error: 'Could not classify — see Logs.',
+}
+function errorTypeColor(t) { return ERROR_TYPE_COLOR[t] || 'error' }
+function errorTypeHint(t) { return ERROR_TYPE_HINT[t] || '' }
 async function onViewLogs(s) {
   if (logLoadingIds.value.has(s.id)) return
   logLoadingIds.value = new Set(logLoadingIds.value).add(s.id)
@@ -115,6 +160,7 @@ async function onViewLogs(s) {
 }
 .fc-fail__artist { font-weight: 600; white-space: nowrap; }
 .fc-fail__count { flex: 0 0 auto; }
+.fc-fail__class { flex: 0 0 auto; }
 .fc-fail__err {
   color: rgb(var(--v-theme-on-surface-variant));
   font-size: 0.8rem;