feat(schema): make note_id and is_reversed NOT NULL

All cards now require note association - legacy card support removed.
This aligns with the note-based card architecture introduced in Phase 8.

- Add database migration for NOT NULL constraints
- Update client Dexie schema to version 3
- Remove LegacyCardItem component and legacy card handling
- Update sync schemas and type definitions
- Update all tests to use note-based cards

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/client/sync/push.ts b/src/client/sync/push.ts
index f5c9275..b83136e 100644
--- a/src/client/sync/push.ts
+++ b/src/client/sync/push.ts
@@ -35,8 +35,8 @@ export interface SyncDeckData {
 export interface SyncCardData {
 	id: string;
 	deckId: string;
-	noteId: string | null;
-	isReversed: boolean | null;
+	noteId: string;
+	isReversed: boolean;
 	front: string;
 	back: string;
 	state: number;