[bmc08gt]

libs:emojis becomes a Kotlin Multiplatform module (flipcash.kmp.app.library, Android + JVM) so Compose Desktop can use the reaction picker and recents. This is the first step toward moving shared/chat to KMP; that follows in the next PR.

• The emoji tables, catalog loader, RecentReactions and the store interface move to commonMain. The first commit is the directory move only, so the second shows the real edits.
• DataStoreRecentReactionsStore takes PreferencesFiles instead of a Context. It still opens recent_reactions with the same keys, and ContextPreferencesFiles resolves to the same path preferencesDataStore used, so existing Android data is read unchanged. ReactionsModule is now in commonMain and takes PreferencesFiles.
• EmojiDrawability keeps its API; the default probe comes from expect fun deviceGlyphProbe(). Android is the same Paint.hasGlyph probe. The JVM actual asks AWT's logical Dialog font whether it can display the string. AWT has no single-glyph check, so a ZWJ sequence a font draws as separate components reads as drawable on desktop.
• EmojiPickerViewModel now calls deviceGlyphProbe() in place of EmojiDrawability.PaintGlyphProbe, which is the only consumer change.
• The emoji generator task writes into src/commonMain/kotlin/.../generated, and compile, KSP and lint tasks depend on it.
• Host tests move to androidHostTest (18 tests, same as before). RecentReactionsStoreTest now gives each test its own temp preferences directory. test-vectors/ is added as a resource directory on the host and device test source sets. The instrumented EmojiDrawabilityVectorTest reads reactions.json from resources instead of assets and moves to androidDeviceTest; it compiles and assembles but I did not run it on a device.
• libs:emojis now depends on :apps:flipcash:core for PreferencesFiles. That pulls firebase's protolite-well-known-types into the device-test classpath, where it duplicates protobuf-javalite classes, so the build excludes it from device-test configurations only.