Fix critical bugs, improve version checking, and add Korean localization

[ava-jahlee]

Summary

• Fix NPE crash when URL fetch fails - wrap Document in Optional, cache failures properly in ConcurrentHashMap
• Semantic version comparison - new versionsMatch/normalizeVersion so v1.0 == 1.0 and 1.0.0 == 1.0 no longer show false update alerts
• Fix regex group validation - check groupCount before accessing capture groups to prevent IndexOutOfBoundsException
• Replace ForkJoinPool with dedicated ExecutorService for HTTP requests to avoid blocking the shared pool
• Replace Timer with ScheduledExecutorService in FXUtils to prevent thread leaks
• Non-blocking rate limiting - replace Thread.sleep in App.processNextMod with ScheduledExecutorService
• Move data directory to ~/.sims4modchecker/ with automatic legacy migration
• Add scraping rules for MCCC, WickedWhims, Basemental, NisaK, Lumpinou, SimRealist
• URL scheme validation in downloadAndSaveImage (only http/https)
• Add Korean localization (i18n_ko.properties)
• Remove unused Gluon plugin, pin Java toolchain to 23, bump version to 1.1

Files Changed (8 files, +248 / -122)

File	Changes
VersionChecker.java	NPE fix, semantic versioning, dedicated thread pool, regex validation
DataManager.java	Data dir migration, new scraping rules, URL validation, logger
App.java	Non-blocking rate limit, semantic version check, Korean UI
FXUtils.java	Timer to ScheduledExecutorService
ModListCell.java	Use new versionsMatch()
AppUtils.java	Korean language mapping
build.gradle	Remove Gluon, pin Java 23, version 1.1
i18n_ko.properties	New Korean translation file

Test Plan

• Build with ./gradlew build (requires Java 23)
• Launch app and verify mod list loads without NPE
• Test version check with mods that have mismatched version formats
• Verify Korean locale displays correctly
• Confirm data files migrate from legacy location to ~/.sims4modchecker/