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/db/index.ts

@@ -54,8 +54,6 @@ export function getDb(): Database {
 	// Migrations for columns added after initial release
 	try { _db.exec('ALTER TABLE stream_decisions ADD COLUMN custom_title TEXT'); } catch { /* already exists */ }
 	try { _db.exec('ALTER TABLE review_plans ADD COLUMN subs_extracted INTEGER NOT NULL DEFAULT 0'); } catch { /* already exists */ }
-	try { _db.exec("ALTER TABLE nodes ADD COLUMN movies_path TEXT NOT NULL DEFAULT ''"); } catch { /* already exists */ }
-	try { _db.exec("ALTER TABLE nodes ADD COLUMN series_path TEXT NOT NULL DEFAULT ''"); } catch { /* already exists */ }
 	try { _db.exec("ALTER TABLE jobs ADD COLUMN job_type TEXT NOT NULL DEFAULT 'audio'"); } catch { /* already exists */ }
 	// Apple compat pipeline columns
 	try { _db.exec("ALTER TABLE review_plans ADD COLUMN confidence TEXT NOT NULL DEFAULT 'low'"); } catch { /* already exists */ }