Add device data model and ITAM service

Introduce device, posture, and enrollment-token entities with ITAM
service policies for agent-managed fleet inventory.

Signed-off-by: Ludovic Vielle <ludovic@probo.com>

pkg/coredata/device_state.go

@@ -0,0 +1,79 @@
+// Copyright (c) 2025-2026 Probo Inc <hello@probo.com>.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+// SOFTWARE.
+
+package coredata
+
+import (
+	"encoding"
+	"fmt"
+)
+
+type DeviceState string
+
+const (
+	DeviceStatePending DeviceState = "PENDING"
+	DeviceStateActive  DeviceState = "ACTIVE"
+	DeviceStateRevoked DeviceState = "REVOKED"
+)
+
+var (
+	_ fmt.Stringer             = DeviceState("")
+	_ encoding.TextMarshaler   = DeviceState("")
+	_ encoding.TextUnmarshaler = (*DeviceState)(nil)
+)
+
+func DeviceStates() []DeviceState {
+	return []DeviceState{
+		DeviceStatePending,
+		DeviceStateActive,
+		DeviceStateRevoked,
+	}
+}
+
+func (v DeviceState) IsValid() bool {
+	switch v {
+	case
+		DeviceStatePending,
+		DeviceStateActive,
+		DeviceStateRevoked:
+		return true
+	}
+
+	return false
+}
+
+func (v DeviceState) String() string {
+	return string(v)
+}
+
+func (v DeviceState) MarshalText() ([]byte, error) {
+	return []byte(v.String()), nil
+}
+
+func (v *DeviceState) UnmarshalText(text []byte) error {
+	val := DeviceState(text)
+	if !val.IsValid() {
+		return fmt.Errorf("invalid DeviceState value: %q", string(text))
+	}
+
+	*v = val
+
+	return nil
+}