fix(telegram): support card — text_mention name, no command/dead link

The topic info card built the profile link as `tg://user?id=`, which
clients render as dead text for a user they don't already know (the
test-vs-prod difference an operator saw), and it put the raw display
name through HTML — so a name starting with "/" was auto-detected as a
tappable bot command that fired when tapped.

Render the card with message entities instead: the display name is
covered by a `text_mention` entity (the reliable way to mention a
username-less user the bot has already seen — it messaged the bot),
which links the profile AND, because the name sits inside an entity,
suppresses the "/command" and "@mention" auto-detection on it. Drop the
HTML parse mode and the tg:// link. Entity offsets are UTF-16.

platform/telegram/README.md

@@ -65,8 +65,9 @@ Telegram identity to an account from a browser. Both map a rejection to gRPC
   `chat_member` updates, which Telegram delivers only to a chat admin.
 - **Support relay (optional).** When `TELEGRAM_SUPPORT_CHAT_ID` names a private **forum
   supergroup**, the bot runs a direct support channel for users who message it. A user's first
-  non-`/start` message opens a dedicated **forum topic** whose first message is an info card (name,
-  @username, language, premium, id, `tg://user` profile link) carrying a **Block/Unblock** toggle
+  non-`/start` message opens a dedicated **forum topic** whose first message is an info card (the
+  name is a tappable profile mention via a `text_mention` entity — which also stops a name starting
+  with `/` from rendering as a command — plus @username, language, premium, id) with a **Block/Unblock** toggle
   and a **Clear** button; each message is then copied into that topic (`copyMessage`, so any content
   — text, media, voice, files — carries over). Any **administrator** of the support chat who writes
   in a user's topic has it copied back to that user; the bot's own posts and non-admins are ignored