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/dashboard/dto.go

@@ -95,6 +95,9 @@ type ipDetailResponse struct {
 	IP     ipQueueItem `json:"ip"`
 	Checks []check     `json:"checks"`
 	Events []event     `json:"events"`
+	// SelfCheckFailedOn lists the validators whose self-check of this address
+	// failed (in its current run).
+	SelfCheckFailedOn []string `json:"self_check_failed_on"`
 }
 
 type validator struct {
@@ -308,6 +311,9 @@ func (t typeStat) Class() string { return statClass(t.OK, t.Total) }
 type registryHistoryResponse struct {
 	Registry registryItem `json:"registry"`
 	Checks   []check      `json:"checks"`
+	// SelfCheckFailedOn lists the validators whose self-check of this address
+	// failed, over every run.
+	SelfCheckFailedOn []string `json:"self_check_failed_on"`
 }
 
 type validatorDTO struct {
@@ -344,6 +350,7 @@ type errorResponse struct {
 type orchestratorSettingsDTO struct {
 	FIPSettleSeconds       int `json:"fip_settle_seconds"`
 	HistoryRetentionCycles int `json:"history_retention_cycles"`
+	SelfCheckMaxAttempts   int `json:"self_check_max_attempts"`
 }
 
 type inboundChecksDTO struct {