Persist per-host scan results and expose hosts endpoint.

Store checked hosts for each scan and add API to fetch host-level up/down probe results.

Made-with: Cursor

internal/store/sql/001_init.sql

@@ -17,3 +17,14 @@ create index if not exists idx_scan_jobs_created_at on scan_jobs (created_at des
 
 alter table scan_jobs add column if not exists progress int not null default 0;
 alter table scan_jobs add column if not exists stats jsonb not null default '{}'::jsonb;
+
+create table if not exists scan_hosts (
+  id bigserial primary key,
+  scan_id text not null references scan_jobs(id) on delete cascade,
+  ip inet not null,
+  is_up boolean not null,
+  checked_at timestamptz not null
+);
+
+create index if not exists idx_scan_hosts_scan_id_checked_at
+  on scan_hosts (scan_id, checked_at desc);