Refactor and modernise app architecture

[baz8080]

Summary

• Menu: Deleted IArcusMenu/ArcusMenu (interface with single implementation, tightly coupled to Activity); replaced with standard XML menu resource and inline handlers
• Constants: Deleted DictionaryConstants bag-of-constants; replaced part-of-speech data with a PartOfSpeech enum, moved remaining constants to their natural homes
• Dead code removed: ArcusDictionaryMockObjects, ArcusFavouritesActivity, unused Pattern field, onActivityResult (was unreachable), onConfigurationChanged, doWarningNoOp
• Preferences: Migrated EditPreferencesActivity from deprecated PreferenceActivity to PreferenceFragmentCompat; removed dead useAutoCorrect preference key
• Initialisation: Made DataFileManager self-contained (stores context at construction); ArcusDictionary.ensureLoaded() no longer needs a context param; ArcusApplication.dictionary is now a by lazy instance property
• Database: Added SortOrder enum to FavouritesDbHelper (closes SQL injection vector from raw sort strings); fixed isFavourite to use SELECT COUNT(*) instead of SELECT *
• View layer bug: WordModel.type changed from var to val; removed mutation of the model inside getView()
• Adapter decoupling: QuickResultListAdapter no longer references ArcusSearchActivity; communicates via a Callbacks interface
• RecyclerView: Replaced ListView and hand-rolled ListAdapter (12 boilerplate methods) with RecyclerView.Adapter + ViewHolder
• Coroutines: Replaced Thread/Handler/Runnable/SearchHandler with lifecycleScope + coroutines
• Back navigation: Replaced deprecated onKeyDown with OnBackPressedCallback
• ViewModel: Added SearchViewModel for sortMethod and previousWord state

Test plan

• Search works with debounce (type, verify results appear after pause)
• Exact match appears at top of results
• Favourites mode: star/unstar words, sort alpha/date, clear all, email
• Back from favourites returns to previous search
• Double-back from search shows exit warning then exits
• Settings screen opens and preferences persist
• TTS speaks selected word
• Share sends word + definition
• App loads correctly on first install (data file extraction)

🤖 Generated with Claude Code