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/components/ContextMenu/GlobalContextMenu.js

@@ -4,6 +4,7 @@ import { translate } from '../../utils/i18nHelpers.js';
 import { state } from '../../state/index.js';
 import { getCompleteApiConfig, getCurrentModelType } from '../../api/apiConfig.js';
 import { performModelUpdateCheck } from '../../utils/updateCheckHelpers.js';
+import { openPriceAlertsPanel, updateService } from '../../managers/UpdateService.js';
 import { rematchModalManager } from '../../managers/RematchModalManager.js';
 import { showRematchSummary } from '../RematchSummaryModal.js';
 
@@ -27,6 +28,7 @@ export class GlobalContextMenu extends BaseContextMenu {
         const excludedModelsItem = this.menu.querySelector('[data-action="manage-excluded-models"]');
         const rematchRecipesItem = this.menu.querySelector('[data-action="rematch-recipes"]');
         const groupByModelItem = this.menu.querySelector('[data-action="toggle-group-by-model"]');
+        const priceAlertsItem = this.menu.querySelector('[data-action="price-alerts"]');
         const groupByModelCheck = groupByModelItem?.querySelector('.check-indicator');
 
         // Update check indicator for group-by-model
@@ -35,6 +37,16 @@ export class GlobalContextMenu extends BaseContextMenu {
             groupByModelCheck.style.display = isEnabled ? 'block' : 'none';
         }
 
+        // Append the unread count when it is already known (loaded once on init,
+        // and only when price tracking is on), so the label stays a plain label
+        // for everyone else.
+        const priceAlertsLabel = priceAlertsItem?.querySelector('#globalPriceAlertsLabel');
+        if (priceAlertsLabel) {
+            const unread = updateService?.getUnreadPriceAlertCount?.() || 0;
+            const base = translate('globalContextMenu.priceAlerts.label', {}, 'Price alerts');
+            priceAlertsLabel.textContent = unread > 0 ? `${base} (${unread})` : base;
+        }
+
         if (isRecipesPage) {
             modelUpdateItem?.classList.add('hidden');
             licenseRefreshItem?.classList.add('hidden');
@@ -42,6 +54,7 @@ export class GlobalContextMenu extends BaseContextMenu {
             cleanupExamplesItem?.classList.add('hidden');
             excludedModelsItem?.classList.add('hidden');
             groupByModelItem?.classList.add('hidden');
+            priceAlertsItem?.classList.add('hidden');
             rematchRecipesItem?.classList.remove('hidden');
         } else {
             modelUpdateItem?.classList.remove('hidden');
@@ -50,6 +63,7 @@ export class GlobalContextMenu extends BaseContextMenu {
             cleanupExamplesItem?.classList.remove('hidden');
             excludedModelsItem?.classList.remove('hidden');
             groupByModelItem?.classList.remove('hidden');
+            priceAlertsItem?.classList.remove('hidden');
             rematchRecipesItem?.classList.add('hidden');
         }
 
@@ -89,6 +103,9 @@ export class GlobalContextMenu extends BaseContextMenu {
                     console.error('Failed to check model updates:', error);
                 });
                 break;
+            case 'price-alerts':
+                openPriceAlertsPanel();
+                break;
             case 'fetch-missing-licenses':
                 this.fetchMissingLicenses(menuItem).catch((error) => {
                     console.error('Failed to refresh missing license metadata:', error);