Retry a failed self-check on another validator; add the self-check failure ceiling

A validator that failed the self-check of an address no longer gets that address
again in the current round (ClaimNextQueued skips it); the validator itself stays
in service and takes all other addresses. The verdict fail is set when the number
of failed self-checks of an address reaches settings.self_check_max_attempts
(1..50, default 5, independent of the number of validators); max_retries and
retry_count are no longer used for self-check. If every working validator has
already failed the address, a new round starts and the exclusions lapse.

Migration 0012: ip_self_check_failures (permanent history per registry address),
ip_queue.sc_failures and sc_round_start_cycle (cycle_id is used instead of
attempt_number, which restarts when a queue row is recreated), the setting.
db.FailSelfCheck does it in one transaction; re-submission starts a new series.
API: self_check_max_attempts in GET/PUT /admin/config/orchestrator,
self_check_failed_on in /admin/ips/{ip} and /admin/registry/{ip}. Dashboard: the
field on /settings and the line "Self-check не прошёл на: ..." on the address
pages. Docs, plan and summary in docs/changes/.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/httpapi/dto_admin.go

@@ -162,12 +162,21 @@ type putCheckTypeRequest struct {
 	Targets []string `json:"targets"`
 }
 
-// orchestratorSettingsDTO doubles as both the GET response and the PUT
-// request body for /api/v1/admin/config/orchestrator — a single-field DTO,
-// same shape both ways, like putSiteRequest/siteDTO.
+// orchestratorSettingsDTO is the GET response for
+// /api/v1/admin/config/orchestrator.
 type orchestratorSettingsDTO struct {
 	FIPSettleSeconds       int `json:"fip_settle_seconds"`
 	HistoryRetentionCycles int `json:"history_retention_cycles"`
+	SelfCheckMaxAttempts   int `json:"self_check_max_attempts"`
+}
+
+// putOrchestratorSettingsRequest is the PUT body. SelfCheckMaxAttempts is a
+// pointer so that a client written before the field existed (it sends only
+// the first two) leaves the ceiling unchanged instead of failing validation.
+type putOrchestratorSettingsRequest struct {
+	FIPSettleSeconds       int  `json:"fip_settle_seconds"`
+	HistoryRetentionCycles int  `json:"history_retention_cycles"`
+	SelfCheckMaxAttempts   *int `json:"self_check_max_attempts"`
 }
 
 // inboundChecksDTO doubles as both the GET response and the PUT request