New external site management. New external prober heartbeat feature.

internal/db/migrations/0005_unbounded_sites.sql

@@ -0,0 +1,19 @@
+-- Remove the hardcoded 3-site limit: ip_queue.site{1,2,3}_complete are
+-- replaced by a child table with no cap on site_idx, keyed by
+-- attempt_number the same way `checks` already is (see docs/USAGE.md).
+
+ALTER TABLE ip_queue DROP COLUMN site1_complete;
+ALTER TABLE ip_queue DROP COLUMN site2_complete;
+ALTER TABLE ip_queue DROP COLUMN site3_complete;
+
+-- Per-IP-per-site inbound-check completion. No fixed cap on site_idx, and
+-- no reset needed on retry — a new attempt_number simply has no rows yet,
+-- unlike the old fixed columns which had to be explicitly zeroed.
+CREATE TABLE ip_site_checks (
+  ip_id          INTEGER NOT NULL REFERENCES ip_queue(id),
+  attempt_number INTEGER NOT NULL,
+  site_idx       INTEGER NOT NULL,
+  complete       BOOLEAN NOT NULL DEFAULT 0,
+  completed_at   TIMESTAMP,
+  PRIMARY KEY (ip_id, attempt_number, site_idx)
+);