fix(sub): {{INBOUND}} = inbound remark, fix {{TRAFFIC_LEFT}} across inbounds (#5443)

Issue 1: the host endpoint remark no longer substitutes the inbound remark
as the config name. {{INBOUND}} always resolves to the inbound's own remark
and {{HOST}} to the host remark, so both can be shown side by side instead
of the host name appearing twice. configName() drops hostRemark entirely;
token help text updated in all locales.

Issue 2: client_traffics.email is globally unique, so a client shared across
several inbounds of one subscription has a single traffic row owned by one
inbound. statsForClient only searched the current inbound's preloaded
ClientStats, missing on every other inbound's link and falling back to
Up=Down=0 -- so {{TRAFFIC_LEFT}} printed the full quota. Build a per-request
email->stats map from all the subscription's inbounds (no extra queries) and
fall back to it.

internal/web/translation/en-US.json

@@ -951,7 +951,7 @@
           "time": "Time & status"
         },
         "descEMAIL": "Client email",
-        "descINBOUND": "Config name: the host's remark when set, otherwise the inbound's remark",
+        "descINBOUND": "Inbound's own remark (the config name)",
         "descHOST": "Host remark",
         "descID": "Client UUID",
         "descSHORT_ID": "First 8 characters of the UUID",