feat: add NFT usernames and bot verification (#22)

Implements collectible usernames, official verification workflows, and third-party bot verification after maintainer protocol and migration review.

The composite activity/moderation rating remains an admin-only read model; Telegram Stars Rating wire fields stay unset pending a dedicated official-semantics implementation.

Reviewed-Head: 2796345775ea0f908fb7734601e5e1dee4b653b9
Original-Head: fa082b892fd5180c9c9bc53c81c21cf5d250a75b

Co-authored-by: Egor Egorov <business.egor.sg@gmail.com>

deploy/migrations/0158_drop_service_account_ratings.up.sql

@@ -0,0 +1,20 @@
+-- Service accounts carry no composite rating.
+--
+-- The rating measures what an account did with Stars, so a bot -- which does not
+-- transact on its own behalf -- and the built-in service accounts -- which are
+-- infrastructure rather than participants -- have no meaningful score. The seeding
+-- pass now excludes both, but the platform account (777000) is not flagged is_bot,
+-- so a deployment that already ran a recompute cycle has a projection row for it
+-- and would show a level badge on the platform account's profile.
+--
+-- Drop those rows and their ledger. The read model is derived, so deleting a row
+-- loses nothing that cannot be recomputed; the ledger rows go with it because a
+-- manual adjustment for an account that can no longer be rated is unreachable
+-- bookkeeping.
+DELETE FROM public.account_rating_events
+WHERE user_id IN (777000, 93372553, 1063110917, 1250000007, 1250000011, 1250000013)
+   OR user_id IN (SELECT id FROM public.users WHERE is_bot);
+
+DELETE FROM public.account_rating
+WHERE user_id IN (777000, 93372553, 1063110917, 1250000007, 1250000011, 1250000013)
+   OR user_id IN (SELECT id FROM public.users WHERE is_bot);