Multi-account support and streaming fixes

- Change LinkedAccount unique constraint to (userId, serviceId, accountId)
- Add linkedAccountId to StreamDestination for per-account targeting
- OAuth callbacks upsert by accountId so different accounts create new rows
- Delete endpoint changed to /providers/accounts/:id
- getDecryptedToken resolves tokens by linkedAccountId instead of serviceId
- /start transition wrapped in try-catch (enableAutoStart compatibility)
- /end always attempts YouTube complete transition regardless of plan status
- autoDetectEndedPlans loads tokens per-destination

src/types/api.ts

@@ -48,7 +48,7 @@ export interface CreateStreamPlanBody {
 }
 
 export interface CreateDestinationBody {
-  serviceId: string;
+  linkedAccountId: string;
   title: string;
   description?: string;
   privacyStatus?: string;
@@ -68,6 +68,7 @@ export interface StreamPlanResponse {
 export interface StreamDestinationResponse {
   id: string;
   serviceId: string;
+  linkedAccountId: string;
   title: string;
   description: string;
   privacyStatus: string;
@@ -85,6 +86,7 @@ export interface PrepareResponse {
 }
 
 export interface PreparedDestination {
+  id: string;
   serviceId: string;
   rtmpUrl: string;
   streamKey: string;