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/i18n/en.json

@@ -133,6 +133,8 @@
 		"authMode": "Authentication Mode",
 		"authModeHint": "Choose hmac_sha256, bearer_token, or none",
 		"genericWebhookSecretHint": "Secret for HMAC-SHA256 or Bearer token authentication. Leave empty for no authentication.",
+		"maxStoredPayloads": "Max stored payloads",
+		"maxStoredPayloadsHint": "Number of recent payloads to keep for debugging (0 = disabled, max 100)",
 		"webhookSecretRequired": "Webhook secret is required",
 		"apiToken": "API Token",
 		"apiTokenHint": "Optional. Needed for connection testing and repository listing.",
@@ -152,11 +154,29 @@
 		"gpRefreshTokenKeep": "Refresh Token (leave empty to keep current)",
 		"gpRefreshTokenHint": "Obtain from Google OAuth Playground (developers.google.com/oauthplayground) with the Photos Library API scope.",
 		"gpAllFieldsRequired": "Client ID, Client Secret, and Refresh Token are all required",
+		"storePayloads": "Store incoming payloads",
+		"storePayloadsHint": "Save recent webhook request bodies for debugging",
+		"maxStoredPayloads": "Max stored payloads",
+		"maxStoredPayloadsHint": "Number of recent payloads to keep (1-100)",
 		"testAndSave": "Test & Save",
 		"saveWithoutTest": "Save without testing",
 		"selectType": "Select a provider type",
 		"testFailed": "Connection test failed"
 	},
+	"webhookLogs": {
+		"title": "Recent Payloads",
+		"empty": "No payloads recorded yet",
+		"clear": "Clear history",
+		"confirmClear": "Clear all stored payloads for this provider?",
+		"statusMatched": "Matched",
+		"statusUnmatched": "Unmatched",
+		"statusError": "Error",
+		"headers": "Headers",
+		"body": "Request Body",
+		"extractedFields": "Extracted Fields",
+		"errorMessage": "Error",
+		"cleared": "Payload history cleared"
+	},
 	"notificationTracker": {
 		"title": "Notification Trackers",
 		"description": "Monitor albums for changes",
@@ -951,6 +971,20 @@
 		"providerGooglePhotos": "Google Photos albums & shared libraries",
 		"providerWebhook": "Receive events via HTTP POST"
 	},
+	"webhookLogs": {
+		"title": "Recent Payloads",
+		"empty": "No payloads recorded yet",
+		"clear": "Clear history",
+		"confirmClear": "Clear all stored payloads for this provider?",
+		"statusMatched": "Matched",
+		"statusUnmatched": "Unmatched",
+		"statusError": "Error",
+		"headers": "Headers",
+		"body": "Request Body",
+		"extractedFields": "Extracted Fields",
+		"errorMessage": "Error",
+		"cleared": "Payload history cleared"
+	},
 	"error": {
 		"notFound": "Page not found",
 		"goHome": "Go home"