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)

packages/server/src/notify_bridge_server/api/providers.py

@@ -99,6 +99,8 @@ class WebhookProviderConfig(BaseModel):
     payload_mappings: list[PayloadMapping] = []
     event_type_path: str | None = None
     collection_path: str | None = None
+    store_payloads: bool = True
+    max_stored_payloads: int = 20  # 1-100
 
 
 _PROVIDER_CONFIG_MODELS: dict[str, type[BaseModel]] = {