v12.18.0

Offline observability: what an app needs to show offline state honestly. Same contract as @koolbase/* 12.14.0.

• Koolbase.connectivity -- KoolbaseConnectivityState.unknown | online | offline, with state and changes. Whether the device reports a connection: a hint, not a promise the server is reachable. unknown until the platform first answers, so an app neither flashes "offline" nor runs online-only logic on a guess.
• watchPendingWrites() follows sign-in and sign-out. It re-reads for the new user (or reports signed out) instead of waiting for the queue to change. db.sessionChanged(), wired to auth by Koolbase.initialize.
• Saved-first record views. db.doc(id).getSaved() returns the device's saved copy (with changes queued on this device applied) without the network. KoolbaseRecordController shows it at once with isSaved true while the server is asked: success replaces it (isSaved false), failure keeps it, not found is notFound. Opening a record offline now shows the saved copy instead of an error.
• Saved lists follow offline changes. An offline add, edit or delete updates the saved lists in place -- an offline add used to drop them entirely -- and an open list that cannot reach the server shows that saved copy (isFromCache true) instead of staying as it was.
• Fix: a second offline edit no longer drops fields. A record with queued edits was projected from the edits alone, so a second offline edit lost every field neither edit touched until the next sync.
• Tested: connectivity, per-user watching across a session change, the chain projection, getSaved, saved lists after an offline add/edit/delete, the open-list fallback, and saved-first in each outcome.