[eduardomazolini]

Closes #3112

Why

Bedrock players joining through Geyser/Floodgate have already been verified by their Xbox account, but AuthMe still
asks them for a password. On a phone keyboard this is a frequent source of trouble: the pre-join dialog times out
while they type the password twice, and auto-capitalization/autocorrect produce "wrong password" kicks. Many Bedrock
players are young kids (as noted in #3112), and we hit exactly this on our school server.

What

Two new options, both disabled by default:

Hooks:
    floodgate:
        autoLogin: false     # log in registered Bedrock players on join, skip the pre-join dialog
        autoRegister: false  # register Bedrock players without an account (random password) and log them in

• FloodgateService asks Floodgate (FloodgateApi#isFloodgatePlayer(UUID)) whether the connecting UUID is a Bedrock
  player. Floodgate is accessed by reflection, the same way PaperDialogFlowListener already talks to ViaVersion, so
  it stays an optional runtime dependency and no new repository/dependency is added to the build.
• PaperDialogFlowListener: skips the pre-join dialog for those players (like the verified premium path).
• AsynchronousJoin: force-logs registered Bedrock players in (next to the premium bypass), or registers them through
  the existing API_REGISTRATION flow with a random password that satisfies the configured length limits.
• Java players are never affected: the decision is based on the UUID Floodgate reports, not on the name prefix, so a
  Java client using a name like .Steve still has to log in.
• docs/config.md regenerated (only the new section kept).

Tests

• New unit tests in AsynchronousJoinTest (auto login without limbo, auto register with a 24-char random password)
  and PaperDialogFlowListenerTest (dialog skipped for registered and unregistered Bedrock players).
• mvn test -am -pl authme-paper-common,authme-paper: 1584 tests, 0 failures.
• Running on a real Paper 26.2 server (Geyser 2.11.3, Floodgate 2.2.5 b141, offline mode, whitelist on) with the
  options enabled:
  • registered Bedrock players joined without any dialog (The Bedrock player .X has been automatically logged in);
  • a new Bedrock player was registered and logged in on first join (... automatically registered);
  • Java players on the same server still got the pre-join login dialog as before.