feat: Implement user preferences management system

- Added user preferences configuration with default values.
- Created API endpoints for retrieving, updating, and managing user preferences.
- Implemented functionality to get specific preferences and acknowledge notifications.
- Introduced walkthrough completion and cancellation features.
- Updated schemas for user preferences to support a flat key-value structure.
- Enhanced UserPreferencesService to handle preference initialization, retrieval, and updates.
- Added validation for preference keys and values to ensure data integrity.

Author: Lasim

services/backend/api-spec.json

@@ -0,0 +1,14 @@
+CREATE TABLE `userPreferences` (
+	`id` text PRIMARY KEY NOT NULL,
+	`user_id` text NOT NULL,
+	`preference_key` text NOT NULL,
+	`preference_value` text NOT NULL,
+	`created_at` integer NOT NULL,
+	`updated_at` integer NOT NULL,
+	FOREIGN KEY (`user_id`) REFERENCES `authUser`(`id`) ON UPDATE no action ON DELETE cascade
+);
+--> statement-breakpoint
+CREATE INDEX `user_preferences_user_key_idx` ON `userPreferences` (`user_id`,`preference_key`);--> statement-breakpoint
+CREATE INDEX `user_preferences_user_idx` ON `userPreferences` (`user_id`);--> statement-breakpoint
+CREATE INDEX `user_preferences_key_idx` ON `userPreferences` (`preference_key`);--> statement-breakpoint
+CREATE INDEX `user_preferences_unique_user_key` ON `userPreferences` (`user_id`,`preference_key`);--> statement-breakpoint