Add SSH key management, job history persistence, and live streaming

- SSH key management: generate ed25519 keypairs or import public keys
  from UI (/ssh-keys), per-machine key selection in Machines form,
  one-time private key download with hash verification
- Fix engine to use machine-specific SSH key (was hardcoded to server key)
- Job log persistence: write to job_logs table (DB) with batched inserts,
  buffer of 50 lines; GetAllFiltered with status/pair/date range filters
- EventBus refactor: per-job subscriber channels, global channel, non-blocking
- SSE endpoints: /jobs/stream (all), /jobs/:id/log/stream (per-job live)
- JobDetail page: live log streaming, auto-scroll, cancel, duration
- JobHistory: filters (pair, status, date range), pagination, link to detail
- Cleanup scheduler: daily purge of job_logs and finished jobs older than
  SYNCSERVER_RETENTION_DAYS (default 30)
- Migration 0002: indexes on job_logs(job_id), jobs(status,created_at),
  jobs(sync_pair_id)

web/src/api/client.ts

@@ -21,6 +21,10 @@ export async function api<T>(path: string, opts: ApiOptions = {}): Promise<T> {
   return res.json();
 }
 
+export async function apiRaw(path: string): Promise<Response> {
+  return fetch(`${BASE}${path}`, { credentials: 'include' });
+}
+
 export interface User {
   id: number;
   username: string;
@@ -64,4 +68,24 @@ export interface Job {
   started_at: string | null;
   finished_at: string | null;
   log_file: string | null;
+  duration_seconds?: number | null;
+  log_line_count?: number | null;
+}
+
+export interface LogLine {
+  id: number;
+  job_id: number;
+  stream: string;
+  content: string;
+  timestamp: string;
+}
+
+export interface SSHKey {
+  id: number;
+  label: string;
+  public_key: string;
+  fingerprint: string;
+  in_use: boolean;
+  has_private_key: boolean;
+  created_at: string;
 }