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/web/service/inbound_node.go

@@ -744,10 +744,12 @@ func (s *InboundService) setRemoteTrafficLocked(nodeID int, snap *runtime.Traffi
 			if err := tx.Exec(
 				fmt.Sprintf(
 					`UPDATE client_traffics
-					 SET up = up + ?, down = down + ?, enable = %s, total = ?,
+					 SET up = %s, down = %s, enable = %s, total = ?,
 					     expiry_time = CASE WHEN expiry_time > 0 AND CAST(? AS BIGINT) <= 0 THEN expiry_time ELSE CAST(? AS BIGINT) END,
 					     reset = ?, last_online = %s
 					 WHERE email = ?`,
+					database.ClampedAddExpr("up"),
+					database.ClampedAddExpr("down"),
 					enableExpr,
 					database.GreatestExpr("last_online", "?"),
 				),