perf: incremental render scale, SQL pagination and observability

- BIRD filter chunking (500 CIDR); bounded job worker pool
- ListModulesPage SQL push-down; revision diff limit; batch revision prune
- DB pool tuning; Prometheus pipeline/job metrics
- Coalesce module_refresh via idempotency; GET /jobs/{id}/report
- JobAuditWriter foundation for job_audit persistence

Co-authored-by: Cursor <[email protected]>

internal/jobs/job.go

@@ -9,6 +9,8 @@ import (
 	"sync"
 	"time"
 
+	"evobgp/internal/observability"
+
 	"github.com/google/uuid"
 )
 
@@ -178,6 +180,7 @@ type Registry struct {
 	byID        map[string]*Job
 	byIdempo    map[idempoKey]*Job
 	workerStart func(j *Job)
+	workerSem   chan struct{}
 }
 
 type idempoKey struct {
@@ -186,13 +189,22 @@ type idempoKey struct {
 }
 
 func NewRegistry(workerStart func(j *Job)) *Registry {
+	maxWorkers := registryMaxConcurrentJobs()
 	return &Registry{
 		byID:        make(map[string]*Job),
 		byIdempo:    make(map[idempoKey]*Job),
 		workerStart: workerStart,
+		workerSem:   make(chan struct{}, maxWorkers),
 	}
 }
 
+func registryMaxConcurrentJobs() int {
+	if n, err := strconv.Atoi(strings.TrimSpace(os.Getenv("EVOBGP_JOB_MAX_CONCURRENT"))); err == nil && n > 0 {
+		return n
+	}
+	return 8
+}
+
 // pruneTerminalIfOver удаляет самые старые завершённые джобы (succeeded/failed/cancelled), пока len(byID) > maxJobs.
 func (r *Registry) pruneTerminalIfOver(maxJobs int) {
 	if r == nil || maxJobs <= 0 || len(r.byID) <= maxJobs {
@@ -244,7 +256,11 @@ func (r *Registry) Enqueue(tenantID, kind string, idempotencyKey *string, module
 	if idempotencyKey != nil && *idempotencyKey != "" {
 		k := idempoKey{tenant: tenantID, key: *idempotencyKey}
 		if existing, ok := r.byIdempo[k]; ok {
-			return existing, false, nil
+			st := existing.statusLocked()
+			if st == StatusQueued || st == StatusRunning {
+				return existing, false, nil
+			}
+			delete(r.byIdempo, k)
 		}
 	}
 
@@ -265,7 +281,17 @@ func (r *Registry) Enqueue(tenantID, kind string, idempotencyKey *string, module
 	r.pruneTerminalIfOver(maxJobs)
 
 	if r.workerStart != nil {
-		go r.workerStart(j)
+		go func() {
+			r.workerSem <- struct{}{}
+			active := len(r.workerSem)
+			capacity := cap(r.workerSem)
+			observability.RecordJobQueueDepth(active, capacity)
+			defer func() {
+				<-r.workerSem
+				observability.RecordJobQueueDepth(len(r.workerSem), capacity)
+			}()
+			r.workerStart(j)
+		}()
 	}
 	return j, true, nil
 }