feat: add Gitea as webhook-based service provider

First webhook-based provider integration (Immich uses polling).
Gitea pushes events via POST /api/webhooks/gitea/{provider_id} with
HMAC-SHA256 signature validation.

- 9 event types: push, issue opened/closed/commented, PR opened/closed/merged/commented, release published
- Generic filters system on NotificationTracker (collections, senders, exclude_senders)
- Provider capabilities include supported_filters and webhook_based flag
- Gitea API client for connection testing and repository listing
- 18 default Jinja2 notification templates (EN + RU)
- Frontend: conditional provider forms, Gitea event toggles in tracking config
- Auto-migration for filters column and Gitea tracking flags

frontend/src/lib/i18n/en.json

@@ -106,11 +106,18 @@
 		"offline": "Offline",
 		"checking": "Checking...",
 		"typeImmich": "Immich",
+		"typeGitea": "Gitea",
 		"loadError": "Failed to load providers.",
 		"externalDomain": "External Domain",
 		"optional": "optional",
 		"urlApiKeyRequired": "URL and API Key are required",
 		"externalDomainHint": "Public-facing URL for notification links. Falls back to server URL.",
+		"webhookSecret": "Webhook Secret",
+		"webhookSecretKeep": "Webhook Secret (leave empty to keep current)",
+		"webhookSecretHint": "Shared secret for HMAC-SHA256 signature verification. Set the same secret in Gitea webhook settings.",
+		"webhookSecretRequired": "Webhook secret is required",
+		"apiToken": "API Token",
+		"apiTokenHint": "Optional. Needed for connection testing and repository listing.",
 		"testAndSave": "Test & Save",
 		"saveWithoutTest": "Save without testing"
 	},
@@ -248,6 +255,7 @@
 		"matrixRoomId": "Room ID",
 		"receivers": "Receivers",
 		"noReceivers": "No receivers yet",
+		"alreadyAdded": "already added",
 		"addReceiver": "Add Receiver",
 		"receiverAdded": "Receiver added",
 		"receiverDeleted": "Receiver deleted",
@@ -348,6 +356,15 @@
 		"albumRenamed": "Album renamed",
 		"albumDeleted": "Album deleted",
 		"sharingChanged": "Sharing changed",
+		"push": "Push",
+		"issueOpened": "Issue opened",
+		"issueClosed": "Issue closed",
+		"issueCommented": "Issue commented",
+		"prOpened": "PR opened",
+		"prClosed": "PR closed",
+		"prMerged": "PR merged",
+		"prCommented": "PR commented",
+		"releasePublished": "Release published",
 		"trackImages": "Track images",
 		"trackVideos": "Track videos",
 		"favoritesOnly": "Favorites only",