Add referral system and user balance tracking

Introduce balance field to User model with Alembic migration. Add
referral menu, admin /refpay command, and deep link sharing. Update
Dockerfile to multi-stage build and add Postgres service to compose.
Fix deep link parsing logic and conditional proxy initialization.

keyboards/client.py

@@ -5,7 +5,7 @@ from config import settings
 from misc.utils import convert_duration_to_int
 from schemas.subscriptions import SubscriptionDuration
 
-main_menu: InlineKeyboardMarkup = InlineKeyboardBuilder(
+main_menu = InlineKeyboardBuilder(
     [
         [
             InlineKeyboardButton(text="⚙️ Купить", callback_data="buy"),
@@ -16,6 +16,7 @@ main_menu: InlineKeyboardMarkup = InlineKeyboardBuilder(
             InlineKeyboardButton(text="Тех. Поддержка", callback_data="support"),
         ],
         [InlineKeyboardButton(text="🔗 Обновить ссылку", callback_data="update_link")],
+        [InlineKeyboardButton(text="👤 Реферальная система", callback_data="referal")],
     ]
 ).as_markup()
 
@@ -23,6 +24,17 @@ _return_to_menu_btn: InlineKeyboardButton = InlineKeyboardButton(
     text="⬅️ Назад", callback_data="menu:main"
 )
 
+return_to_menu: InlineKeyboardMarkup = InlineKeyboardBuilder(
+    [[_return_to_menu_btn]]
+).as_markup()
+
+payment_gateways: InlineKeyboardMarkup = InlineKeyboardBuilder(
+    [
+        [InlineKeyboardButton(text="✍️ Перейти в поддержку", callback_data="checkout")],
+        [_return_to_menu_btn],
+    ]
+).as_markup()
+
 
 def _return_btn(
     data: str = "menu:main", text: str = "⬅️ Назад"
@@ -30,11 +42,6 @@ def _return_btn(
     return InlineKeyboardButton(text=text, callback_data=data)
 
 
-return_to_menu: InlineKeyboardMarkup = InlineKeyboardBuilder(
-    [[_return_to_menu_btn]]
-).as_markup()
-
-
 def devices_selector(current: int = settings.min_devices, whitelists: bool = False):
     builder = InlineKeyboardBuilder()
 
@@ -89,9 +96,10 @@ def duration_selector(
     return builder.as_markup()
 
 
-payment_gateways: InlineKeyboardMarkup = InlineKeyboardBuilder(
-    [
-        [InlineKeyboardButton(text="✍️ Перейти в поддержку", callback_data="checkout")],
-        [_return_to_menu_btn],
-    ]
-).as_markup()
+def referals_kb(share_link: str) -> InlineKeyboardMarkup:
+    return InlineKeyboardBuilder(
+        [
+            [InlineKeyboardButton(text="🔗 Поделиться ссылкой", url=share_link)],
+            [_return_to_menu_btn],
+        ]
+    ).as_markup()