Feat v0.3.0 workflow schema redesign + stage CRUD modernization

Drop chat-era columns (persona_id, history_mode) from workflow_stages.
Rename transition_rules → stage_config. Add audience, stage_type,
starlark_hook, branch_rules columns. Update stage_mode CHECK to
(form, review, delegated, automated). All Go stores, handlers,
routing engine, Starlark module, and frontend editors updated.

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

server/models/workflow.go

@@ -54,13 +54,15 @@ type WorkflowStage struct {
 	WorkflowID       string          `json:"workflow_id"`
 	Ordinal          int             `json:"ordinal"`
 	Name             string          `json:"name"`
-	PersonaID        *string         `json:"persona_id,omitempty"`
 	AssignmentTeamID *string         `json:"assignment_team_id,omitempty"`
 	FormTemplate     json.RawMessage `json:"form_template"`
-	StageMode        string          `json:"stage_mode"`   // form_only | form_chat | review | custom
-	HistoryMode      string          `json:"history_mode"` // full | summary | fresh
+	StageMode        string          `json:"stage_mode"`  // form | review | delegated | automated
+	Audience         string          `json:"audience"`    // team | public | system
+	StageType        string          `json:"stage_type"`  // simple | dynamic | automated
 	AutoTransition   bool            `json:"auto_transition"`
-	TransitionRules  json.RawMessage `json:"transition_rules"`
+	StageConfig      json.RawMessage `json:"stage_config"`
+	BranchRules      json.RawMessage `json:"branch_rules"`
+	StarlarkHook     *string         `json:"starlark_hook,omitempty"`
 	SurfacePkgID     *string         `json:"surface_pkg_id,omitempty"`
 	SLASeconds       *int            `json:"sla_seconds,omitempty"`
 	CreatedAt        time.Time       `json:"created_at"`
@@ -69,18 +71,48 @@ type WorkflowStage struct {
 // ── Stage Mode Constants ────────────────────
 
 const (
-	StageModeCustom   = "custom"
-	StageModeFormOnly = "form_only"
-	StageModeFormChat = "form_chat"
-	StageModeReview   = "review"
+	StageModeForm      = "form"
+	StageModeReview    = "review"
+	StageModeDelegated = "delegated"
+	StageModeAutomated = "automated"
 )
 
 // ValidStageModes is the set of valid stage_mode values.
 var ValidStageModes = map[string]bool{
-	StageModeCustom:   true,
-	StageModeFormOnly: true,
-	StageModeFormChat: true,
-	StageModeReview:   true,
+	StageModeForm:      true,
+	StageModeReview:    true,
+	StageModeDelegated: true,
+	StageModeAutomated: true,
+}
+
+// ── Stage Type Constants ────────────────────
+
+const (
+	StageTypeSimple    = "simple"
+	StageTypeDynamic   = "dynamic"
+	StageTypeAutomated = "automated"
+)
+
+// ValidStageTypes is the set of valid stage_type values.
+var ValidStageTypes = map[string]bool{
+	StageTypeSimple:    true,
+	StageTypeDynamic:   true,
+	StageTypeAutomated: true,
+}
+
+// ── Audience Constants ──────────────────────
+
+const (
+	AudienceTeam   = "team"
+	AudiencePublic = "public"
+	AudienceSystem = "system"
+)
+
+// ValidAudiences is the set of valid audience values.
+var ValidAudiences = map[string]bool{
+	AudienceTeam:   true,
+	AudiencePublic: true,
+	AudienceSystem: true,
 }
 
 // ── Typed Form Template ─────────────────────