Add robust date parsing and simplify lesson selection logic. Introduces ISO8601 formatters (with and without fractional seconds) and updates parseNextSchoolDayDate to try both variants, plus existing yyyy-MM-dd fallback. Adds LessonCandidate, startOfDay and nextSchoolDay helpers and builds a sorted candidate list (today, tomorrow, next school day) to pick the appropriate lesson set and correctly set isNextDay/isNextSchoolDay flags. Cleans up previous branching-heavy logic and improves handling of edge cases (lessons finished, next-school-day resolution).
Several watch UI and sync improvements: clamp CountdownRing values and use clamped values for progress/color/display; add optional backgroundColor to FirkaCard and refactor HomeView to use lessonTitleWithStatus, lessonCardBackgroundColor and improved break time calculation and refresh handling (onChange of lastUpdated). TimetableView now shows status icons/colors via helper methods. DataStore now returns a localized "time_now" for recent updates. WatchSessionManager handles Flutter channel/unready states by serving shared language state when available and avoids empty language replies. Dart fixes: await initLang in settings, return null from WatchSyncHelper when uninitialized, and attempt to publish language to watch after initialization in main.
Replace index-based loops with zip(entry.lessons, entry.lessons.dropFirst()) in TimetableMediumView and TimetableLargeView to iterate adjacent lesson pairs. This improves readability and safety (avoids manual index arithmetic and potential out-of-bounds issues) while keeping the same break-detection logic.
Introduce shared session and language state plus cross-device refresh leases to improve Watch/iPhone sync. Adds SharedSessionStateManager, SharedLanguageStateManager and RefreshLeaseManager (keychain-backed) and exposes accessGroup via SharedKeychainManager. Wire shared state into WatchSessionManager (publish/load language and session state, immediate token send via message + userInfo + applicationContext, reachability check, lease-related Flutter handlers) and into WatchConnectivityManager (parse versions, apply immediate token updates). Update DataStore and WatchL10n to reconcile shared session/language state, handle stale account switching, and request tokens from phone when needed. Add TokenManager watch-side lease wrapper for refresh coordination, UI tweaks for pairing/no-token messages and icons, small fixes (date parsing in widget provider, background refresh cadence to ~15 min, time-since localization keys and usage), and various helper utilities for parsing int64 and state versioning.
