merge: sync LeanBitLab v3.9.5

[AsafMah]

Summary

This updates the existing upstream-sync PR to merge LeanBitLab/LeanType v3.9.5 into LeanTypeDual, pinned at release tag commit 8cfe7f1fc and including the still-unmerged v3.9.3/v3.9.4 syncs.

The v3.9.5 delta adds direct switching to a configured IME/subtype, persistent custom-layout state, a multi-word suggestion filter, and the v3.9.5 release notes. 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 prior v3.9.3/v3.9.4 conflict resolutions and the fallback suggestion-casing fix already on this PR.
• Adopted upstream v3.9.5's canonical custom-layout codes CUSTOM1..CUSTOM5 = -10081..-10085 and direct-switch code SWITCH_TO_USER_IME = -10076 after auditing the entire fork KeyCode table for collisions.
• The global KeySpecParserTest.keyCodeValuesAreUnique regression passes with those values.
• Reviewed Mergiraf's README/FEATURES resolutions; direct-IME and custom-layout documentation was added once while retaining the fork feature guide.
• Centralized all three multi-word filtering paths onto one tested helper.
• Updated the Unreleased changelog with one cumulative ### Upstream marker for v3.9.5 (including v3.9.3/v3.9.4).

Independent review follow-up

A high-effort independent review completed and raised custom-layout persistence and missing coverage concerns. Code ownership inspection showed savedKeyboardState and lastCustomIndex share the same persistent KeyboardState instance; a real lifecycle regression test now locks that behavior down. The temporary -10100..-10104 values existed only on this still-unmerged PR, so no released-user migration is required when adopting v3.9.5's canonical values.

Added focused coverage for:

• CUSTOM2 → symbols → save/load → alphabet restoring CUSTOM2
• direct IME empty/missing no-op
• external IME absent/invalid subtype fallback through switchInputMethod(id)
• valid external IME + subtype switching
• same-IME internal subtype selection
• enabled/disabled multi-word suggestion filtering shared by normal, gesture, and next-word paths
• full-suite-safe shared IMM shadow fixtures with per-test reset

The review follow-up request timed out, and a bounded fallback reviewer was unavailable/cancelled; the concrete findings from the completed review were nevertheless investigated and covered by passing regression tests.

Verification

Compile gates:

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

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

Focused regressions:

KeyboardStateTest
DirectImeSwitchTest
SuggestTest.multi-word filter removes phrases only when enabled
KeySpecParserTest.keyCodeValuesAreUnique

All focused tests pass, both alone and in the full suite.

Offline unit differential:

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

Branch	Tests	Failed	Skipped
pre-v3.9.5 PR baseline f09e33591	278	11	1
v3.9.5 updated merge	284	12	1

All 11 baseline failing names remain unchanged. The additional failure is XLinkTest.knownDictionaries, where an unchanged randomized external Codeberg URL (main_bn_bd.dict) currently returns 404; the asset/test source is identical on baseline and current. The six new behavioral tests pass.

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.