merge: sync LeanBitLab v3.9.4

[AsafMah]

Summary

This updates the existing upstream-sync PR to merge LeanBitLab/LeanType v3.9.4 into LeanTypeDual, pinned at release tag commit 56034a695 and including the still-unmerged v3.9.3 sync.

The v3.9.4 delta adds custom secondary layouts, configurable auto-correct triggers, text-expander placeholder fixes, gesture-engine memory/performance improvements, and dictionary/blacklist hardening. LeanTypeDual's fork identity remains unchanged: application id com.asafmah.leantypedual, version 3.10.0 / 4000, and no network permission in offline/offlinelite builds.

Integration notes

• Kept LeanTypeDual version, application id, branding, privacy tiers, and fork-specific settings/features.
• Preserved the v3.9.3 conflict resolutions already reviewed in this PR.
• Reviewed Mergiraf's v3.9.4 resolutions in LayoutType.kt and SwipeGestureEngine.java.
• Fixed a downstream integration collision: upstream's new CUSTOM1..CUSTOM5 values reused -10010..-10014, which LeanTypeDual already uses for PageUp/PageDown/Meta/MetaLock/Tab. Custom layout codes now use unique -10100..-10104 values.
• Added KeySpecParserTest.keyCodeValuesAreUnique to prevent future runtime KeyCode collisions.
• Updated the Unreleased changelog with one cumulative ### Upstream marker for v3.9.4 (including v3.9.3).

Verification

Compile gates:

./gradlew.bat compileOfflineRunTestsKotlin --no-daemon --console=plain
BUILD SUCCESSFUL

./gradlew.bat compileStandardRunTestsKotlin compileStandardfullRunTestsKotlin compileOfflineliteRunTestsKotlin --no-daemon --console=plain
BUILD SUCCESSFUL

KeyCode regression:

./gradlew.bat :app:testOfflineDebugUnitTest --tests "*KeySpecParserTest.keyCodeValuesAreUnique" --no-daemon --console=plain
BUILD SUCCESSFUL

Offline unit differential:

./gradlew.bat :app:testOfflineDebugUnitTest --continue --no-daemon --console=plain

Branch	Tests	Failed	Skipped
v3.9.3 PR baseline 8e761e1fb	274	12	1
v3.9.4 updated merge 18ad76470	276	11	1

All 11 current failing test names already fail on the v3.9.3 baseline. There are no new failures. Baseline-only XLinkTest.knownDictionaries (external 404) now passes, and the suite gained two tests.

Permission check:

app/src/standard/AndroidManifest.xml: android.permission.INTERNET
app/src/standardfull/AndroidManifest.xml: android.permission.INTERNET

No INTERNET permission is present in offline/offlinelite manifests.