feat(dashboard): add Phase 3 database queries for Carousel-style dashboard

Add SQL queries for dashboard functionality and system collections:

Dashboard Preferences Queries:
- GetDashboardPreferences: Fetch user preferences for a library
- UpsertDashboardPreferences: Create or update user dashboard preferences
- UpdateDashboardPreferences: Update existing preferences

Dashboard Collections Queries:
- GetSystemCollectionsForDashboard: Fetch system collections (user_id IS NULL)
- GetUserCollectionsForDashboard: Fetch user collections marked for dashboard
- DeleteUserSystemCollection: Delete user's copy of a system collection

System Collection Smart Queries:
- GetContinueReadingItems: Books with 0 < progress < 1
- GetRecentlyAddedItems: Newly added items to library
- GetRecentlyReadItems: Books with progress >= 1
- GetNotStartedItems: Books with progress = 0 or no record

Collection Management Queries:
- GetCollectionItemsForDashboard: Fetch collection items with excluded flag
- GetLibraryItems: Fetch all items in a library

These queries support the unified collections architecture where system
defaults and user-created sections are both collections with user_id
NULL for system-owned and NOT NULL for user-created.

internal/database/queries/queries.sql

@@ -1588,3 +1588,103 @@ JOIN devices d ON ub.device_id = d.id
 WHERE ub.resolved = false
 ORDER BY ub.last_seen_at DESC
 LIMIT $1 OFFSET $2;
+
+-- ============================================
+-- CAROUSEL-STYLE DASHBOARD
+-- ============================================
+
+-- Dashboard preferences queries
+-- name: GetDashboardPreferences :one
+SELECT * FROM user_dashboard_preferences
+WHERE user_id = $1 AND library_id = $2;
+
+-- name: UpsertDashboardPreferences :one
+INSERT INTO user_dashboard_preferences (user_id, library_id, hidden_collections, collection_order, items_per_section)
+VALUES ($1, $2, $3, $4, $5)
+ON CONFLICT (user_id, library_id)
+DO UPDATE SET
+    hidden_collections = EXCLUDED.hidden_collections,
+    collection_order = EXCLUDED.collection_order,
+    items_per_section = EXCLUDED.items_per_section,
+    updated_at = NOW()
+RETURNING *;
+
+-- name: UpdateDashboardPreferences :one
+UPDATE user_dashboard_preferences
+SET hidden_collections = $2,
+    collection_order = $3,
+    items_per_section = $4,
+    updated_at = NOW()
+WHERE user_id = $1 AND library_id = $5
+RETURNING *;
+
+-- Dashboard collections queries
+-- name: GetSystemCollectionsForDashboard :many
+SELECT * FROM collections
+WHERE user_id IS NULL
+  AND show_on_dashboard = true
+ORDER BY priority ASC;
+
+-- name: GetUserCollectionsForDashboard :many
+SELECT c.* FROM collections c
+WHERE c.user_id = $1
+  AND c.show_on_dashboard = true
+  AND c.is_system_collection = false
+ORDER BY priority ASC;
+
+-- name: DeleteUserSystemCollection :exec
+DELETE FROM collections
+WHERE user_id = $1
+  AND name = $2
+  AND is_system_collection = true;
+
+-- Smart section queries (for system collections)
+-- name: GetContinueReadingItems :many
+SELECT DISTINCT mi.* FROM media_items mi
+INNER JOIN reading_progress rp ON rp.media_item_id = mi.id
+WHERE mi.library_id = $1
+  AND rp.user_id = $2
+  AND rp.percentage > 0
+  AND rp.percentage < 1
+ORDER BY rp.last_read_at DESC
+LIMIT $3;
+
+-- name: GetRecentlyAddedItems :many
+SELECT mi.* FROM media_items mi
+WHERE mi.library_id = $1
+ORDER BY mi.created_at DESC
+LIMIT $2;
+
+-- name: GetRecentlyReadItems :many
+SELECT DISTINCT mi.* FROM media_items mi
+INNER JOIN reading_progress rp ON rp.media_item_id = mi.id
+WHERE mi.library_id = $1
+  AND rp.user_id = $2
+  AND rp.percentage >= 1
+ORDER BY rp.last_read_at DESC
+LIMIT $3;
+
+-- name: GetNotStartedItems :many
+SELECT mi.* FROM media_items mi
+WHERE mi.library_id = $1
+  AND NOT EXISTS (
+    SELECT 1 FROM reading_progress rp
+    WHERE rp.media_item_id = mi.id
+      AND rp.user_id = $2
+      AND rp.percentage > 0
+  )
+ORDER BY mi.created_at DESC
+LIMIT $3;
+
+-- name: GetCollectionItemsForDashboard :many
+SELECT mi.*, ci.excluded FROM media_items mi
+INNER JOIN collection_items ci ON ci.media_item_id = mi.id
+WHERE ci.collection_id = $1
+  AND mi.library_id = $2
+ORDER BY ci.added_at DESC
+LIMIT $3;
+
+-- name: GetLibraryItems :many
+SELECT mi.* FROM media_items mi
+WHERE mi.library_id = $1
+ORDER BY mi.created_at DESC;