feat: custom brand name everywhere + a working client-facing site out of the box

User ask, paraphrased: install it, get help wiring up payments, and
immediately have a ready site under your own name — not "MBS Panel"
plastered everywhere and a bunch of manual follow-up.

Two things were actually broken/missing, found by tracing every surface
a real customer or the operator would see:

1. "MBS Panel" was hardcoded in ~20 places (bot messages, subscription
   page, admin panel splash/title/sidebar, legal pages, 2FA issuer,
   install.sh) with zero way to change it short of editing source.
   New BRAND_NAME config value (config.py default "MBS Panel", so this
   is 100% backward compatible for existing installs) wired through
   everywhere via the same live-settings pattern from the last commit
   (settings.get_brand_name(), no restart needed anywhere it's used).
   New Настройки → «Название» section in the admin panel to change it.

2. site/index.html and site/cabinet.html — a fully-built landing page +
   personal-cabinet template, already in the repo — were never actually
   served by anything. Not mounted by FastAPI, not deployed by
   install.sh, not linked from anywhere. Pure dead weight: a repo that
   looked like it shipped a client site but didn't. Now legal.py gets a
   render_site_page() (same {{TOKEN}} substitution + HTML-escaping as
   the existing offer/privacy renderer, new tokens: BRAND_NAME,
   SITE_DOMAIN, SUB_DOMAIN, BOT_USERNAME) and GET "/" serves the branded
   landing page on any host that isn't PANEL_DOMAIN (in practice:
   SUB_DOMAIN, which nginx already routes to this backend — zero
   install.sh/nginx/certbot changes needed, so this is live on every
   existing install without an upgrade step beyond `mbs update`).
   GET /cabinet.html serves the cabinet. Landing page's pricing section
   now fetches real, live prices from a new public GET /api/plans
   instead of showing static duration labels with no numbers.

Also fixed along the way, same staleness-bug class as the payments/HWID
fix last commit, found by grepping for every remaining frozen `from
config import ...` in api.py: BOT_TOKEN/BOT_USERNAME were still frozen
constants in api.py (mbs-api never restarts itself). Concretely this
meant: changing the bot via Настройки → Telegram-бот would leave
_tg_send_message (payment-received notifications) silently trying the
OLD token, admin_get_bot_settings showing the OLD username right after
a successful save, and gift-code links pointing at the OLD bot — all
until a manual mbs restart, same shape as the Platega-secret bug fixed
last commit. Added settings.bot_credentials(), wired it through every
call site (hoisted out of loops where relevant, same N+1 discipline as
always), removed the now-stale "выполни mbs restart" copy from the bot
settings hint.

legal.py's own BOT_USERNAME import was frozen too (used by the /offer
and /privacy {{BOT_USERNAME}} token) — switched to reading it live
in-module (no settings.py import from legal.py, would've been circular
since settings.py already imports legal.py for the env reader).

install.sh: new interactive prompt for the brand name (default "MBS
Panel", so hitting enter reproduces today's behavior exactly), written
to .env, echoed in the final summary along with the now-live site URL.

Verification: same story as always — api.py/bot.py still can't import
locally (no pydantic-core wheel for Python 3.14 on this machine).
py_compile + pyflakes clean across the whole repo. Real runtime test
against an isolated .env fixture: brand name and bot-credential live
reads (no reimport), render_site_page() token substitution correctness
on the actual site/index.html and site/cabinet.html files including an
XSS check (brand name containing <script> comes out HTML-escaped), and
a regression check that adding the BRAND_NAME token to the existing
legal.render() didn't break offer.html/privacy.html. Extracted
SUB_PAGE_TEMPLATE/SUB_PAGE_EXPIRED_TEMPLATE via ast from api.py (can't
import the module, but can pull the string constants) and ran the real
.format() calls against them to catch any brace-escaping mistake in the
new {brand_name} placeholder — CSS braces in those templates are
already double-escaped for .format(), easy to get wrong. Extracted and
node --check'd admin.html's whole inline script, div-tag-balance check
on the full file. install.sh's new prompt+heredoc snippet run standalone
with piped stdin (both a brand name with spaces and an empty/default
input), round-tripped the resulting .env back through the real
env-parsing logic. Extended the existing CI "app wiring" step (which
does import api/bot for real on Linux) with branding assertions calling
the actual route functions directly (api.root(), api.public_plans(),
api.public_branding()) — ran every part of that step's new logic that
doesn't need api.py locally first, to catch what's catchable before
trusting the rest to CI once the account's abuse-review lifts.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

bot.py

@@ -72,13 +72,14 @@ def connect_kb(token: str, extra_rows: list[list[InlineKeyboardButton]] | None =
     return InlineKeyboardMarkup(inline_keyboard=rows)
 
 
-ABOUT_TEXT = (
-    "<b>MBS Panel</b>\n\n"
-    "Быстрый и незаметный доступ без границ. Протокол VLESS+Reality "
-    "маскируется под обычный HTTPS-трафик, ничем не палится.\n\n"
-    f"{DIVIDER}\n"
-    f"Сайт: {SITE_DOMAIN}"
-)
+def about_text() -> str:
+    return (
+        f"<b>{settings.get_brand_name()}</b>\n\n"
+        "Быстрый и незаметный доступ без границ. Протокол VLESS+Reality "
+        "маскируется под обычный HTTPS-трафик, ничем не палится.\n\n"
+        f"{DIVIDER}\n"
+        f"Сайт: {SITE_DOMAIN}"
+    )
 
 
 async def send_main_menu(message: Message):
@@ -121,7 +122,7 @@ async def start_deeplink(message: Message, command: CommandObject):
 async def start_plain(message: Message):
     db.get_or_create_user(message.from_user.id, message.from_user.username)
     await message.answer(
-        "Привет! Это бот MBS Panel.\nВыбери действие ниже.",
+        f"Привет! Это бот {settings.get_brand_name()}.\nВыбери действие ниже.",
     )
     await send_main_menu(message)
 
@@ -135,7 +136,7 @@ async def cb_menu_main(cb: CallbackQuery):
 @dp.callback_query(F.data == "menu:about")
 async def cb_about(cb: CallbackQuery):
     kb = InlineKeyboardMarkup(inline_keyboard=[[InlineKeyboardButton(text="Назад", callback_data="menu:main")]])
-    await cb.message.edit_text(ABOUT_TEXT, reply_markup=kb)
+    await cb.message.edit_text(about_text(), reply_markup=kb)
     await cb.answer()
 
 
@@ -201,7 +202,7 @@ async def cb_pay(cb: CallbackQuery):
     db.create_payment(payment_id, cb.from_user.id, node_code, plan_code, provider, plan["price"])
     try:
         external_id, pay_url = payments.create_payment_link(
-            provider, payment_id, plan["price"], f"MBS Panel — {node_row['label']}, {plan['label']}",
+            provider, payment_id, plan["price"], f"{settings.get_brand_name()} — {node_row['label']}, {plan['label']}",
         )
     except Exception:
         log.exception("payment creation failed")