feat(maintenance): add policy executor and config provider

ConfigProvider, PolicyExecutor, DBStatsProvider, scheduler и safety; зависимость robfig/cron/v3.

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

internal/maintenance/db_stats_provider.go

@@ -0,0 +1,62 @@
+package maintenance
+
+import (
+	"context"
+	"fmt"
+
+	"evobgp/internal/pgmonitor"
+)
+
+// TableHints are PostgreSQL statistics hints for UI recommendations.
+type TableHints struct {
+	TableName       string   `json:"table_name"`
+	DeadTuples      int64    `json:"n_dead_tup"`
+	BloatRatio      float64  `json:"bloat_ratio,omitempty"`
+	LastAutovacuum  string   `json:"last_autovacuum,omitempty"`
+	RecommendVacuum bool     `json:"recommend_vacuum"`
+	Detail          string   `json:"detail,omitempty"`
+	Refs            []string `json:"refs,omitempty"`
+}
+
+// DBStatsProvider wraps pgmonitor for maintenance policy hints.
+type DBStatsProvider struct {
+	pg *pgmonitor.Service
+}
+
+// NewDBStatsProvider constructs a stats provider.
+func NewDBStatsProvider(pg *pgmonitor.Service) *DBStatsProvider {
+	return &DBStatsProvider{pg: pg}
+}
+
+// Hints returns table-level vacuum/bloat hints.
+func (d *DBStatsProvider) Hints(ctx context.Context, tableName string) (TableHints, error) {
+	out := TableHints{TableName: tableName}
+	if d == nil || d.pg == nil {
+		return out, fmt.Errorf("maintenance: postgres monitoring not configured")
+	}
+	if err := ValidateTableName(tableName); err != nil {
+		return out, err
+	}
+	tables, err := d.pg.Tables(ctx, 100)
+	if err != nil {
+		return out, err
+	}
+	for _, t := range tables {
+		if t.Relname != tableName {
+			continue
+		}
+		out.DeadTuples = t.DeadTuples
+		out.BloatRatio = t.BloatRatio
+		if t.LastAutovacuum != nil {
+			out.LastAutovacuum = t.LastAutovacuum.UTC().Format("2006-01-02T15:04:05Z")
+		}
+		if t.BloatRatio > 0.2 && t.DeadTuples > 5000 {
+			out.RecommendVacuum = true
+			out.Detail = "Высокая доля n_dead_tup; рекомендуется VACUUM."
+			out.Refs = []string{t.Relname}
+		}
+		return out, nil
+	}
+	out.Detail = "Таблица не найдена в pg_stat_user_tables (top by size)."
+	return out, nil
+}