Move leaderboards into speedrun modes

[matteopolak]

Summary

• add a dedicated Leaderboard tab inside the Speedrun mode switcher
• preserve the old side-by-side Target Practice and Movement Only ranking layout
• remove the redundant top-level Leaderboard tab and keep map layout ownership centralized in ModeContainer
• preserve existing leaderboard refresh behavior and add scene-structure regression coverage

Test plan

• ./scripts/test-godot.sh
• pre-push server quality, server tests/build, website build, Godot suite, and E2E smoke test

[vasiltop]

It looks really bad, would it be possible to move it into its own tab? like in the ModeSwitcher node? this might require a bit of refactor to do but It would look a lot better closer to the old style

[matteopolak]

It looks really bad, would it be possible to move it into its own tab? like in the ModeSwitcher node?

Reworked in bde200c: Speedrun now has a dedicated nested Leaderboard tab using the old side-by-side Target Practice and Movement Only layout. The temporary duplicated map-layout scene trees were also removed, with ModeContainer restored as the single owner of map layout.