Fix crash after the game reaches the menu (null versionInfo)

[ChimeraAnt-DEV]

What this fixes

The launcher shows its crash screen after the game reaches the menu. That screen is
ErrorActivity, reached either from the JVM exit callback or from the app's uncaught
exception handler — so something really is dying, not just failing to render.

Version.getVersionInfo() returns VersionInfo?. It is null whenever the version's
<name>.json is missing or fails to parse, while the version directory itself still exists
on disk. Three call sites dereferenced it with !!:

Site	When it runs
LauncherElements.TryLaunch	reads minecraftVersion before doing anything else
GameHandler.execute (pre-1.13 key fixups)	as the game screen opens
GameHandler.execute (loadLanguage)	as the game screen opens

The GameHandler ones fire as the game screen is being set up, which matches the reported
timing: the game gets far enough to look like it is starting, then dies.

The fix

All three now degrade instead of throwing.

• The launch path checks versionInfo up front and emits a new
  LaunchGameOperation.InvalidVersion, which sends the user to version management with an
  explanation. Previously this was an unhandled NPE.
• GameHandler skips the two version-dependent fixups when the version number is unknown.
  Neither is needed to start the game: one is a pre-1.13 keybind workaround, the other picks
  a language file.

The new string is added to values/, values-zh-rCN/, and values-zh-rTW/.

Also included

AGENTS.md — build notes, the launch pipeline layout, and the getVersionInfo() null
semantics so this class of bug is easier to avoid next time.

Verification

I could not compile or run this: the dev container has no JDK and no Android SDK
(java is not installed), and there is no attached device. The changes were verified by
reading: LaunchGameOperation is a sealed interface whose when in LauncherElements.kt
is exhaustive, so the new case had to be handled and is; no remaining getVersionInfo()!!
exists in the launch or game-screen paths.

Please build and run this against the version that was crashing to confirm.

Scope note

This is a null-safety fix for a real crash, and it is separate from the earlier
cracked/offline-account work. If your crash happens with a version whose JSON is intact,
this will not be the cause, and I would need the crash log from ErrorActivity to go
further.

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By ChimeraTeam