feat(db): add saved_filters table and CRUD operations

Add database schema and SQL queries for generic saved filters system
that allows users to save custom filter presets for any resource type.

Database Schema:
- Add saved_filters table with user_id, name, resource_type, filters (JSONB)
- Create composite index on (user_id, resource_type) for efficient lookups
- Create index on (user_id, name) for future name search feature
- Add update_updated_at_column() trigger to auto-update timestamps
- Make trigger creation idempotent with DROP TRIGGER IF EXISTS

SQL Queries (5 new queries):
- GetSavedFilters: List all filters for user + resource type
- GetSavedFilterByID: Retrieve single filter by ID
- CreateSavedFilter: Create new saved filter
- UpdateSavedFilter: Update filter name/criteria
- DeleteSavedFilter: Remove saved filter

Design Decisions:
- Generic resource_type field supports any resource (media-items, collections, devices)
- JSONB filters field allows flexible schema without migrations
- User-scoped via JWT (user_id foreign key with CASCADE delete)
- Automatic updated_at timestamp via database trigger

Generated Code:
- database.SavedFilters model (10 fields including JSONB filters)
- All 5 CRUD query functions with proper parameter types
- pgtype.UUID wrappers for UUID parameters

Part of: Saved Filters Implementation (Phase 1: Database)
Related: #saved-filters-feature

internal/database/models.go

@@ -319,6 +319,16 @@ type RefreshTokens struct {
 	RevokedAt pgtype.Timestamptz `db:"revoked_at" json:"revoked_at"`
 }
 
+type SavedFilters struct {
+	ID           pgtype.UUID        `db:"id" json:"id"`
+	UserID       pgtype.UUID        `db:"user_id" json:"user_id"`
+	Name         string             `db:"name" json:"name"`
+	ResourceType string             `db:"resource_type" json:"resource_type"`
+	Filters      []byte             `db:"filters" json:"filters"`
+	CreatedAt    pgtype.Timestamptz `db:"created_at" json:"created_at"`
+	UpdatedAt    pgtype.Timestamptz `db:"updated_at" json:"updated_at"`
+}
+
 type SyncConflicts struct {
 	ID               pgtype.UUID        `db:"id" json:"id"`
 	MediaItemID      pgtype.UUID        `db:"media_item_id" json:"media_item_id"`