chore: bump workflow-plugin-agent to v0.6.15

Interactive PTY as primary mode with no exec fallback.
Claude Code + Copilot multi-turn sessions working.

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

Author: intel352

go.mod

@@ -7,7 +7,7 @@ require (
 	charm.land/bubbletea/v2 v2.0.1
 	charm.land/lipgloss/v2 v2.0.0
 	github.com/GoCodeAlone/workflow v0.3.56
-	github.com/GoCodeAlone/workflow-plugin-agent v0.6.14
+	github.com/GoCodeAlone/workflow-plugin-agent v0.6.15
 	github.com/charmbracelet/glamour v0.10.0
 	github.com/coder/acp-go-sdk v0.6.3
 	github.com/creack/pty v1.1.24

go.sum

@@ -68,8 +68,8 @@ github.com/GoCodeAlone/modular/modules/scheduler v1.14.0 h1:JSrzo4FB7uGASExv+fCL
 github.com/GoCodeAlone/modular/modules/scheduler v1.14.0/go.mod h1:emkR2AnilabLJZv1rOTDO9eGpRBmZs487H00Lnp9jIc=
 github.com/GoCodeAlone/workflow v0.3.56 h1:jsJmVwCRLz7XOTLQNoyE7POBDW3SmqbG/18VnAzbaEc=
 github.com/GoCodeAlone/workflow v0.3.56/go.mod h1:uATRqpqPubm+g2jJtYoaMTMmjlUaXnLsSdZk5of+jW0=
-github.com/GoCodeAlone/workflow-plugin-agent v0.6.14 h1:IfabHGqrNAWkiOz0zSO4dHH2T/EK/IeV1z++KPTemak=
-github.com/GoCodeAlone/workflow-plugin-agent v0.6.14/go.mod h1:E/Q8WAKJnC/oFnWkPHJYEqsDCRRqqW0AuxtQdmv6uKg=
+github.com/GoCodeAlone/workflow-plugin-agent v0.6.15 h1:dg4okJMoUz94BabVcJucY+bDZ28D8x5DxtbPAW4quUw=
+github.com/GoCodeAlone/workflow-plugin-agent v0.6.15/go.mod h1:E/Q8WAKJnC/oFnWkPHJYEqsDCRRqqW0AuxtQdmv6uKg=
 github.com/GoCodeAlone/workflow-plugin-authz v0.2.2 h1:xnaNLQybNv4u/TeC1+pJuwUHbLPZaCOtcWcUn4HVeq4=
 github.com/GoCodeAlone/workflow-plugin-authz v0.2.2/go.mod h1:jyeRNdNl8qCXwTc1lGYPazz97ZjCVrE2OGgqGheBJV0=
 github.com/GoCodeAlone/yaegi v0.17.1 h1:aPAwU29L9cGceRAff02c5pjQcT5KapDB4fWFZK9tElE=