fix(db): clamp traffic counters below int64 max and repair overflowed rows

A counter pushed past int64 (multi-node setups hit this via historic
delta-compounding bugs) makes SQLite silently promote the INTEGER cell
to REAL. From then on the column no longer scans into the Go int64
field and every reader of client_traffics fails at once: the inbounds
page, xray restarts, and node traffic sync all return "converting
driver.Value type float64 to int64".

Two-part fix: every unbounded "up = up + ?" add (local traffic, node
delta merge, inbound counters, plus the Go-side outbound accumulation)
now saturates at TrafficMax, a cap safely below math.MaxInt64 so one
more delta cannot overflow; and a startup repair casts REAL-promoted
cells back to INTEGER and clamps all traffic counters into
[0, TrafficMax] across client_traffics, inbounds, outbound_traffics
and node_client_traffics, restoring access to already-corrupted panels
without manual sqlite surgery.

Closes #5762

internal/database/dialect.go

@@ -2,6 +2,19 @@ package database
 
 import "fmt"
 
+// TrafficMax caps every traffic counter safely below math.MaxInt64 (~9.22e18)
+// so that one more delta can never overflow int64. SQLite silently promotes an
+// overflowing INTEGER to REAL, after which the column no longer scans into the
+// Go int64 field and every reader of the table fails (#5762).
+const TrafficMax = int64(9_000_000_000_000_000_000)
+
+func ClampedAddExpr(col string) string {
+	if IsPostgres() {
+		return fmt.Sprintf("LEAST(%s + ?, %d)", col, TrafficMax)
+	}
+	return fmt.Sprintf("MIN(%s + ?, %d)", col, TrafficMax)
+}
+
 func JSONClientsFromInbound() string {
 	if IsPostgres() {
 		return "FROM inbounds, jsonb_array_elements(inbounds.settings::jsonb -> 'clients') AS client(value)"