Initial implementation of inventree

A small IT asset inventory system built around a nested folder tree,
matching the project brief: Go + html/template + Bootstrap 5 + vanilla JS,
SQLite storage (WAL, FKs, migrations), embedded templates/static assets,
single compiled binary.

- AJAX-driven inventory tree: lazy-loaded folder expansion with per-user
  persisted expand state, drag-and-drop move for folders/assets, safe
  delete-with-relocate-or-cascade confirmation, search with breadcrumbs.
- Assets: CRUD, duplicate, move, auto-generated IT-000001-style IDs,
  CSV import (with optional folder auto-create) and export.
- Admin-defined item types with custom fields (text/long_text/number/date/
  boolean/dropdown/url/ip_address).
- Configurable statuses, session-based auth (bcrypt, secure cookies),
  admin/user roles, user management.
- CLI: serve, version, database migrate, database backup; /healthz;
  graceful shutdown; Dockerfile/docker-compose/systemd unit; Go test suite.

internal/models/models.go

@@ -0,0 +1,173 @@
+// Package models defines the core domain types shared across inventree.
+package models
+
+import "time"
+
+type Role string
+
+const (
+	RoleAdmin Role = "admin"
+	RoleUser  Role = "user"
+)
+
+type User struct {
+	ID           int64
+	Username     string
+	PasswordHash string
+	Role         Role
+	Enabled      bool
+	CreatedAt    time.Time
+	UpdatedAt    time.Time
+}
+
+func (u User) IsAdmin() bool { return u.Role == RoleAdmin }
+
+type Folder struct {
+	ID          int64
+	Name        string
+	ParentID    *int64
+	Description string
+	Icon        string
+	SortOrder   int
+	CreatedAt   time.Time
+	UpdatedAt   time.Time
+
+	// Populated by list/tree queries; not persisted directly on this table.
+	FolderCount int
+	AssetCount  int
+}
+
+type Status struct {
+	ID        int64
+	Name      string
+	Color     string
+	SortOrder int
+	CreatedAt time.Time
+	UpdatedAt time.Time
+}
+
+type FieldType string
+
+const (
+	FieldTypeText      FieldType = "text"
+	FieldTypeLongText  FieldType = "long_text"
+	FieldTypeNumber    FieldType = "number"
+	FieldTypeDate      FieldType = "date"
+	FieldTypeBoolean   FieldType = "boolean"
+	FieldTypeDropdown  FieldType = "dropdown"
+	FieldTypeURL       FieldType = "url"
+	FieldTypeIPAddress FieldType = "ip_address"
+)
+
+var AllFieldTypes = []FieldType{
+	FieldTypeText, FieldTypeLongText, FieldTypeNumber, FieldTypeDate,
+	FieldTypeBoolean, FieldTypeDropdown, FieldTypeURL, FieldTypeIPAddress,
+}
+
+func (t FieldType) Label() string {
+	switch t {
+	case FieldTypeText:
+		return "Text"
+	case FieldTypeLongText:
+		return "Long Text"
+	case FieldTypeNumber:
+		return "Number"
+	case FieldTypeDate:
+		return "Date"
+	case FieldTypeBoolean:
+		return "Boolean"
+	case FieldTypeDropdown:
+		return "Dropdown"
+	case FieldTypeURL:
+		return "URL"
+	case FieldTypeIPAddress:
+		return "IP Address"
+	}
+	return string(t)
+}
+
+type ItemType struct {
+	ID          int64
+	Name        string
+	Description string
+	Icon        string
+	Enabled     bool
+	SortOrder   int
+	CreatedAt   time.Time
+	UpdatedAt   time.Time
+
+	Fields []CustomFieldDef
+}
+
+type CustomFieldDef struct {
+	ID           int64
+	ItemTypeID   int64
+	Name         string
+	FieldKey     string
+	FieldType    FieldType
+	Required     bool
+	DefaultValue string
+	Options      []string
+	SortOrder    int
+	CreatedAt    time.Time
+	UpdatedAt    time.Time
+}
+
+type CustomFieldValue struct {
+	ID         int64
+	AssetID    int64
+	FieldDefID int64
+	Value      string
+}
+
+type Asset struct {
+	ID             int64
+	AssetTag       string
+	Name           string
+	ItemTypeID     int64
+	FolderID       *int64
+	StatusID       int64
+	AssignedUserID *int64
+	Notes          string
+	CreatedAt      time.Time
+	UpdatedAt      time.Time
+
+	// Populated by joined list/detail queries.
+	ItemTypeName     string
+	ItemTypeIcon     string
+	StatusName       string
+	StatusColor      string
+	AssignedUsername string
+	FolderPath       []BreadcrumbItem
+	CustomFields     []AssetFieldValue
+}
+
+type AssetFieldValue struct {
+	Def   CustomFieldDef
+	Value string
+}
+
+type BreadcrumbItem struct {
+	ID   int64
+	Name string
+}
+
+// TreeNode is a folder-or-asset node used to render the inventory tree.
+type TreeNode struct {
+	Type        string // "folder" or "asset"
+	ID          int64
+	Name        string
+	Icon        string
+	ParentID    *int64
+	HasChildren bool
+	AssetTag    string
+	StatusName  string
+	StatusColor string
+
+	// Populated only when the node is pre-expanded for server-side
+	// recursive rendering (see web.buildTree); empty otherwise, in which
+	// case the client lazy-loads children via /app/tree/children.
+	Expanded   bool
+	Children   []TreeNode
+	MoreAssets int // count of additional assets beyond the tree display cap, if any
+}