schema(dashboard): implement Phase 1 unified collections architecture

Add support for Carousel-style dashboard with unified collections architecture:

Database Schema Changes:
- Add user_dashboard_preferences table:
  - hidden_collections: TEXT[] for managing section visibility
  - collection_order: TEXT[] for custom ordering
  - items_per_section: INT for limiting items per section
- Update collections table:
  - user_id: Make nullable to support system-owned collections (NULL = system)
  - show_on_dashboard: BOOLEAN for controlling visibility
  - query_type: TEXT for different query types (continue-reading, recently-added, etc.)
  - priority: INT for display order (lower = higher priority)
  - is_system_collection: BOOLEAN for flagging system defaults
- Update collection_items table:
  - Add excluded BOOLEAN for user overrides of auto-assigned items

Indexes:
- idx_collections_dashboard: (user_id, show_on_dashboard, priority) WHERE show_on_dashboard = true
- idx_dashboard_prefs_user_library: (user_id, library_id)
- idx_collection_items_excluded: (collection_id, excluded) WHERE excluded = true

System Collections (pre-seeded defaults):
- continue-reading: Books with 0 < progress < 1
- recently-added: Newly added items to library
- recently-read: Books with progress >= 1
- not-started: Books with progress = 0 or no record

This implements Phase 1 of the Carousel-style dashboard redesign plan.

internal/database/models.go

@@ -14,18 +14,23 @@ type CollectionItems struct {
 	MediaItemID   pgtype.UUID        `db:"media_item_id" json:"media_item_id"`
 	AddedAt       pgtype.Timestamptz `db:"added_at" json:"added_at"`
 	AddedByUserID pgtype.UUID        `db:"added_by_user_id" json:"added_by_user_id"`
+	Excluded      pgtype.Bool        `db:"excluded" json:"excluded"`
 }
 
 type Collections struct {
-	ID              pgtype.UUID        `db:"id" json:"id"`
-	UserID          pgtype.UUID        `db:"user_id" json:"user_id"`
-	Name            string             `db:"name" json:"name"`
-	Description     pgtype.Text        `db:"description" json:"description"`
-	Color           pgtype.Text        `db:"color" json:"color"`
-	Icon            pgtype.Text        `db:"icon" json:"icon"`
-	AutoAssignRules []byte             `db:"auto_assign_rules" json:"auto_assign_rules"`
-	ViewSettings    []byte             `db:"view_settings" json:"view_settings"`
-	CreatedAt       pgtype.Timestamptz `db:"created_at" json:"created_at"`
+	ID                 pgtype.UUID        `db:"id" json:"id"`
+	UserID             pgtype.UUID        `db:"user_id" json:"user_id"`
+	Name               string             `db:"name" json:"name"`
+	Description        pgtype.Text        `db:"description" json:"description"`
+	Color              pgtype.Text        `db:"color" json:"color"`
+	Icon               pgtype.Text        `db:"icon" json:"icon"`
+	AutoAssignRules    []byte             `db:"auto_assign_rules" json:"auto_assign_rules"`
+	ViewSettings       []byte             `db:"view_settings" json:"view_settings"`
+	ShowOnDashboard    pgtype.Bool        `db:"show_on_dashboard" json:"show_on_dashboard"`
+	QueryType          pgtype.Text        `db:"query_type" json:"query_type"`
+	Priority           pgtype.Int4        `db:"priority" json:"priority"`
+	IsSystemCollection pgtype.Bool        `db:"is_system_collection" json:"is_system_collection"`
+	CreatedAt          pgtype.Timestamptz `db:"created_at" json:"created_at"`
 }
 
 type DeviceCatalogs struct {
@@ -373,6 +378,17 @@ type UnlinkedBooks struct {
 	CreatedAt        pgtype.Timestamptz `db:"created_at" json:"created_at"`
 }
 
+type UserDashboardPreferences struct {
+	ID                pgtype.UUID        `db:"id" json:"id"`
+	UserID            pgtype.UUID        `db:"user_id" json:"user_id"`
+	LibraryID         pgtype.UUID        `db:"library_id" json:"library_id"`
+	HiddenCollections []string           `db:"hidden_collections" json:"hidden_collections"`
+	CollectionOrder   []string           `db:"collection_order" json:"collection_order"`
+	ItemsPerSection   pgtype.Int4        `db:"items_per_section" json:"items_per_section"`
+	CreatedAt         pgtype.Timestamptz `db:"created_at" json:"created_at"`
+	UpdatedAt         pgtype.Timestamptz `db:"updated_at" json:"updated_at"`
+}
+
 type Users struct {
 	ID           pgtype.UUID        `db:"id" json:"id"`
 	Email        string             `db:"email" json:"email"`