M2: improve error messages with actionable suggestions

udisks2 connection and device listing errors now suggest checking the
service. Device-not-found errors suggest 'arca status' or 'arca init'.
Failed cryptsetup token unlock hints at missing FIDO2/TPM2 key.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

internal/udisks/client.go

@@ -16,7 +16,7 @@ type Client struct {
 func NewClient() (*Client, error) {
 	conn, err := dbus.SystemBus()
 	if err != nil {
-		return nil, fmt.Errorf("connecting to system bus: %w", err)
+		return nil, fmt.Errorf("cannot connect to udisks2 — is the udisks2 service running? (%w)", err)
 	}
 	return &Client{conn: conn}, nil
 }
@@ -39,7 +39,7 @@ func (c *Client) FindDevice(uuid, pathOrName string) (*BlockDevice, error) {
 				return &devices[i], nil
 			}
 		}
-		return nil, fmt.Errorf("no device with UUID %s", uuid)
+		return nil, fmt.Errorf("no device with UUID %s — run 'arca status' to list devices", uuid)
 	}
 
 	for i := range devices {
@@ -47,7 +47,7 @@ func (c *Client) FindDevice(uuid, pathOrName string) (*BlockDevice, error) {
 			return &devices[i], nil
 		}
 	}
-	return nil, fmt.Errorf("device %s not found", pathOrName)
+	return nil, fmt.Errorf("device %s not found — run 'arca status' to list devices or 'arca init' to generate config", pathOrName)
 }
 
 // ListEncryptedDevices returns all block devices with the Encrypted interface.
@@ -152,7 +152,7 @@ func (c *Client) listBlockDevices() ([]BlockDevice, error) {
 	var managed map[dbus.ObjectPath]map[string]map[string]dbus.Variant
 	err := obj.Call(ifaceObjectManager+".GetManagedObjects", 0).Store(&managed)
 	if err != nil {
-		return nil, fmt.Errorf("listing devices: %w", err)
+		return nil, fmt.Errorf("listing devices — is the udisks2 service running? (%w)", err)
 	}
 
 	var devices []BlockDevice