docs: bake Telegram invite & launch refinements into ARCHITECTURE/UI_DESIGN

- UI_DESIGN: mobile immersive fullscreen on launch (desktop keeps full-size); the
  close confirmation is now mobile-only; friend-code share-via-Telegram deep-link
  (per-bot, by service language), the friendly self-redeem note, and the
  outdated-link lobby notice.
- ARCHITECTURE: the service language rides the Session wire so the client builds
  the per-bot invite link; the friend code is shared as a startapp deep-link with
  graceful spent/expired handling.

docs/ARCHITECTURE.md

@@ -151,7 +151,9 @@ arrive from a platform rather than completing a mandatory registration).
   login — last-login-wins) and routes the user's out-of-app push back through the right
   bot (§10) — **except a game event, which routes by the game's own language** (its variant →
   en/ru), so a game's notification always comes from the game's bot rather than the
-  recipient's latest login bot. The service language is distinct from `preferred_language` (the
+  recipient's latest login bot. It also rides the **Session wire** to the client, which uses it
+  to build the friend-invite **share link** (and its caption) for the **same bot** the player
+  is in. The service language is distinct from `preferred_language` (the
   interface language) and from a game's variant language. Non-Telegram logins (web / email / guest) carry the
   gateway's default set (`GATEWAY_DEFAULT_SUPPORTED_LANGUAGES`, all variants by default).
 - The client holds `session_id` in memory for the app session (browser/OS
@@ -425,7 +427,11 @@ English game the Latin pool.
 - **Friends**: two add paths over one `friendships` table. A **one-time
   code** the to-be-added player issues (a `friend_codes` row: 6-digit numeric,
   SHA-256-hashed, **12 h** TTL, one live code per issuer, single-use, redeem
-  rate-limited) is redeemed by the other player to become friends immediately.
+  rate-limited) is redeemed by the other player to become friends immediately. It is shared as
+  a Telegram `startapp` deep-link to the issuer's own bot (by service language, with a matching
+  caption), redeemed by the recipient's Mini App on launch; a **spent or expired** code is not
+  surfaced as an error there but lands the visitor in the lobby with a gentle pointer to the
+  right bot, since the shared link outlives the single-use code.
   Alternatively a **request → accept** is sent to someone you **share a game with**
   (active or finished); the recipient may accept, ignore (the pending row lazily
   expires after **30 days** and may be re-sent), or **decline** — a decline is

docs/UI_DESIGN.md

@@ -67,8 +67,12 @@ Login uses `Screen`.
   theme switcher is hidden; the nav bar takes Telegram's background and `setHeaderColor` /
   `setBackgroundColor` / `setBottomBarColor` paint Telegram's own chrome to match; the
   native header **BackButton** drives back-navigation (the app's chevron is hidden in
-  Telegram); **HapticFeedback** fires on tile placement / commit / error; **closing
-  confirmation** is enabled while a game is open; **vertical swipes** (swipe-to-minimise)
+  Telegram); **HapticFeedback** fires on tile placement / commit / error; on **mobile**
+  clients the app enters **immersive fullscreen** on launch (`requestFullscreen`, Bot API
+  8.0+) like Telegram's own Mini Apps, while desktop keeps the bot's full-size window;
+  **closing confirmation** is enabled while a game is open **on mobile only** (on desktop
+  closing is deliberate and the "changes may not be saved" dialog is just noise — move drafts
+  auto-save); **vertical swipes** (swipe-to-minimise)
   are disabled so they don't fight tile drag or the board scroll; and a live stream dropped
   by a background suspend reconnects silently on return — the connection banner is
   suppressed while hidden and for a short grace after resume (visibilitychange +
@@ -242,8 +246,14 @@ IV 🏅; active games show Your move 🟢 / Opponent's move ⏳; invitations use
   every field is valid. Interface language stays in **Settings** (it writes through to
   the account for durable users).
 - **Friend code**: the issued code sits next to a 📋 copy control; tapping the code or
-  the icon copies it. Flex text inputs carry `min-width:0` so they shrink instead of
-  overflowing in Safari.
+  the icon copies it. **Share via Telegram** wraps the code in a `t.me/<bot>/<app>?startapp=`
+  deep-link and opens Telegram's native share-to-chat sheet (Web Share / clipboard fallback
+  outside Telegram); the link and its caption are for the **same bot the player signed in
+  through** (its service language). Redeeming your **own** invite shows a friendly note, not an
+  error; opening an **outdated** invite link (a used or expired single-use code) lands in the
+  lobby with a calm modal pointing at the right bot (`@<username>`), not a red error on the
+  Friends tab. Flex text inputs carry `min-width:0` so they shrink instead of overflowing in
+  Safari.
 - **History / GCG**: the in-game slide-down history lays each move out in a per-seat grid
   (the word(s) and the move score, no running total); *Export GCG* (the 📤 in the history
   header) shares or downloads the `.gcg` file and appears only once the game is finished.