Adds the wire schema for the eight `user.games.mail.*` ConnectRPC
commands together with the shared payload types (`MailMessage`,
`MailRecipientState`, `MailBroadcastReceipt`). Send-request tables
carry the optional `recipient_race_name` introduced in Step 1.
Drops:
- `pkg/schema/fbs/diplomail.fbs` — schema sources;
- `pkg/schema/fbs/diplomail/*.go` — generated Go bindings (flatc
`--go --go-module-name galaxy/schema/fbs`);
- `pkg/model/diplomail/diplomail.go` — message-type catalog used by
the gateway router;
- `ui/frontend/src/proto/galaxy/fbs/diplomail/*.ts` — generated TS
bindings consumed by the upcoming UI client wrapper;
- `ui/Makefile` `FBS_INPUTS` extended to pick the new schema up on
the next `make -C ui fbs-ts` run.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Ilia Denisov