drop multi-node ssh execution, unify job runner to local + fix job completion atomicity

- remove nodes table, ssh service, nodes api, NodesPage route
- execute.ts: local-only spawn, atomic CAS job claim via UPDATE status
- wrap job done + subtitle_files insert + review_plans status in db transaction
- stream ffmpeg output per line with 500ms throttled flush
- bump version to 2026.04.13

server/types.ts

@@ -84,7 +84,6 @@ export interface Job {
 	item_id: number;
 	command: string;
 	job_type: 'copy' | 'transcode';
-	node_id: number | null;
 	status: 'pending' | 'running' | 'done' | 'error';
 	output: string | null;
 	exit_code: number | null;
@@ -93,22 +92,6 @@ export interface Job {
 	completed_at: string | null;
 }
 
-export interface Node {
-	id: number;
-	name: string;
-	host: string;
-	port: number;
-	username: string;
-	private_key: string;
-	ffmpeg_path: string;
-	work_dir: string;
-	movies_path: string;
-	series_path: string;
-	status: 'unknown' | 'ok' | 'error';
-	last_checked_at: string | null;
-	created_at: string;
-}
-
 // ─── Analyzer types ───────────────────────────────────────────────────────────
 
 export interface StreamWithDecision extends MediaStream {