feat(sidebar+groups): available-channels above channel-status; show rate for subscription groups

- Sidebar user-side order: /available-channels now sits directly above
  /monitor (渠道状态) for regular users, mirroring the admin section where
  it sits above /admin/channels.
- GroupBadge gains an alwaysShowRate prop. Subscription groups default to
  a "订阅"/days-remaining label; the new flag swaps that for the rate
  multiplier while keeping the subscription theme color, so the Available
  Channels page can surface rates on every group type.

frontend/src/components/channels/AvailableChannelsTable.vue

@@ -83,6 +83,7 @@
               :subscription-type="(g.subscription_type || 'standard') as SubscriptionType"
               :rate-multiplier="g.rate_multiplier"
               :user-rate-multiplier="userGroupRates[g.id] ?? null"
+              always-show-rate
             />
           </div>
           <div
@@ -104,6 +105,7 @@
               :subscription-type="(g.subscription_type || 'standard') as SubscriptionType"
               :rate-multiplier="g.rate_multiplier"
               :user-rate-multiplier="userGroupRates[g.id] ?? null"
+              always-show-rate
             />
           </div>
           <span v-if="section.groups.length === 0" class="text-xs text-gray-400">-</span>