feat(update): add a Buzz price alerts panel to the notification bell

P5a of docs/plans/paid-model-price-tracking.md: one surface that answers "what
got cheaper / became free", without a permanent button (the grid filter was
dropped by owner decision, so the panel carries the actions itself).

- price_alert_since records when an alert started, so the panel can say
  "dropped 3 d ago" and count what is new since the user last looked; it is set
  on the first sight of an already-cheap version, preserved while the alert
  stands, and cleared when the price rises back above the threshold
- get_price_alerts() compares the threshold at read time (editing it takes
  effect immediately, no refresh needed) and returns both kinds in one list;
  model_type=None covers every type, which the shared update DB makes a single
  query. "became free" needs no price data, so it is reported even while price
  tracking is off
- GET /api/lm/price-alerts, registered once in MiscRoutes rather than per model
  type, decorating rows best-effort with the local model name and file path from
  the scanner indexes (a cold cache just omits them)
- a third tab in the notification bell: segments for under-threshold and
  became-free, the three states (tracking off / nothing matching / stale), and
  per-row actions (CivitAI always, Open when the model is local)
- two non-permanent entry points share one helper: the controls-bar updates
  dropdown and the global context menu, whose label carries the unread count
- unread state stays client-side (localStorage watermark); the count is fetched
  once on init and only when price tracking is enabled
- the per-type frontend client method is removed as dead code; the per-type
  backend route stays for the companion extension

static/js/api/apiConfig.js

@@ -98,7 +98,9 @@ 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`,
+
+        // Price alerts are app-wide (all model types in one query), so they are
+        // not part of this per-type endpoint map; see UpdateService.js.
 
         // Preview management
         replacePreview: `/api/lm/${modelType}/replace-preview`,

static/js/api/baseModelApi.js

@@ -1086,33 +1086,6 @@ 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');