feat(update): track buzz prices and alert below a threshold

CivitAI's public API deliberately omits prices — paidAccess is trimmed to
{permanent, endsAt} because "pricing belongs to the purchase flow" — but the
public model page embeds the site's own model.getById result, including
paidAccess.terms, in its server-rendered payload. That is read anonymously
(no API key, no internal endpoint, no forged Origin), one request per gated
model, so only the ~2% of models that actually carry a gate pay for it.

- optional capture, off by default: price_tracking_enabled,
  price_alert_threshold_buzz (0 = alert on "became free" only) and
  price_check_ttl_hours; prices refresh on their own TTL and immediately when a
  gate changes, and a failed fetch keeps the stored price instead of blanking it
- versions that stop carrying a gate are marked free (persisted gate_lapsed_at)
  and gate transitions are reported as events on the refresh response, so a
  version already in the library can announce that it became free
- price_alert_state plus a price_drop edge event; new
  GET /api/lm/{type}/updates/price-alerts lists what is under the threshold
- versions tab shows the price (effective, with the list price struck through
  and a Blue Buzz note) and a Free Now badge; an update check toasts the
  transitions in one message
- the parser and the alerts query are unit-tested against a trimmed page
  fixture, and every route definition is now asserted to resolve to a handler

Plan, verification notes and the deviations from it are in
docs/plans/paid-model-price-tracking.md.

static/js/api/apiConfig.js

@@ -98,6 +98,7 @@ export function getApiEndpoints(modelType) {
         modelUpdateVersions: `/api/lm/${modelType}/updates/versions`,
         ignoreModelUpdate: `/api/lm/${modelType}/updates/ignore`,
         ignoreVersionUpdate: `/api/lm/${modelType}/updates/ignore-version`,
+        priceAlerts: `/api/lm/${modelType}/updates/price-alerts`,
 
         // Preview management
         replacePreview: `/api/lm/${modelType}/replace-preview`,

static/js/api/baseModelApi.js

@@ -1086,6 +1086,33 @@ export class BaseModelApiClient {
         }
     }
 
+    /**
+     * Versions whose stored price currently crosses the alert threshold.
+     * Backed by the persisted alert state, so it matches the version badges.
+     * @param {{limit?: number}} [options]
+     * @returns {Promise<{alerts: Array, thresholdBuzz: number, enabled: boolean}>}
+     */
+    async getPriceAlerts({ limit = 200 } = {}) {
+        const endpoint = this.apiConfig?.endpoints?.priceAlerts;
+        if (!endpoint) {
+            return { alerts: [], thresholdBuzz: 0, enabled: false };
+        }
+
+        const response = await fetch(`${endpoint}?limit=${encodeURIComponent(limit)}`, {
+            method: 'GET'
+        });
+        const payload = await response.json().catch(() => ({}));
+        if (!response.ok || payload?.success !== true) {
+            throw new Error(payload?.error || response.statusText || 'Failed to load price alerts');
+        }
+
+        return {
+            alerts: Array.isArray(payload.alerts) ? payload.alerts : [],
+            thresholdBuzz: payload.thresholdBuzz ?? 0,
+            enabled: payload.enabled === true
+        };
+    }
+
     async refreshUpdatesForModels(modelIds, { force = false } = {}) {
         if (!Array.isArray(modelIds) || modelIds.length === 0) {
             throw new Error('No model IDs provided');