feat: webhook payload history — store and display recent incoming payloads

Backend:
- WebhookPayloadLog model (provider_id, method, headers, body, status, extracted_fields, error_message)
- Auto-log payloads in generic_webhook() with matched/unmatched/error status
- Auto-prune beyond max_stored_payloads per provider
- Header filtering (only Content-Type, User-Agent, X-* stored; no Authorization)
- GET/DELETE /api/providers/{id}/webhook-logs endpoints
- store_payloads + max_stored_payloads in WebhookProviderConfig

Frontend:
- WebhookPayloadHistory.svelte — expandable log viewer with status badges, JSON body, headers, extracted fields
- payloadHistory flag on webhook provider descriptor
- max_stored_payloads config field (0 = disabled)
- Password confirmation field on change password modal
- i18n keys for webhook logs (en + ru)

frontend/src/lib/providers/types.ts

@@ -139,6 +139,8 @@ export interface ProviderDescriptor {
 	// ── Webhook URL display ──
 	/** Pattern shown in edit mode, e.g. "/api/webhooks/gitea/{id}". */
 	webhookUrlPattern?: string;
+	/** Whether this provider stores incoming payload history for debugging. */
+	payloadHistory?: boolean;
 
 	// ── Provider-specific hooks ──
 	/**

frontend/src/lib/providers/webhook.ts

@@ -21,12 +21,22 @@ export const webhookDescriptor: ProviderDescriptor = {
 			type: 'password', optional: true,
 			hint: 'providers.genericWebhookSecretHint',
 		},
+		{
+			key: 'max_stored_payloads', configKey: 'max_stored_payloads',
+			label: 'providers.maxStoredPayloads',
+			type: 'number',
+			min: 0, max: 100,
+			defaultValue: 20,
+			hint: 'providers.maxStoredPayloadsHint',
+		},
 	],
 
 	buildConfig(form, editing) {
 		const config: Record<string, any> = {
 			auth_mode: form.auth_mode || 'none',
 			payload_mappings: form.payload_mappings || [],
+			store_payloads: form.store_payloads !== '0' && form.store_payloads !== 0,
+			max_stored_payloads: Math.max(1, Math.min(100, Number(form.max_stored_payloads) || 20)),
 		};
 		if (form.webhook_secret) config.webhook_secret = form.webhook_secret;
 		if (form.event_type_path) config.event_type_path = form.event_type_path;
@@ -36,7 +46,9 @@ export const webhookDescriptor: ProviderDescriptor = {
 
 	hasConfigChanged(form, existing) {
 		return form.auth_mode !== (existing.auth_mode || 'none') ||
-			!!form.webhook_secret;
+			!!form.webhook_secret ||
+			(form.store_payloads !== '0' && form.store_payloads !== 0) !== (existing.store_payloads !== false) ||
+			Number(form.max_stored_payloads || 20) !== Number(existing.max_stored_payloads || 20);
 	},
 
 	eventFields: [
@@ -46,4 +58,5 @@ export const webhookDescriptor: ProviderDescriptor = {
 	collectionMeta: null,
 	webhookBased: true,
 	webhookUrlPattern: '/api/webhooks/webhook/{id}',
+	payloadHistory: true,
 };