feat(mcp): delete tasks, create task lists and lists, agent badge; export/import settings category

New MCP tools delete_task (tasks:write), create_task_list (tasks:write) and create_list
(lists:write); list_task_lists now returns the board columns so agents know the valid
kanbanStatus values. Task deletion is a shared helper (deleteTask) for REST and MCP.

Tasks and list items get agent_mark (migration 12): "created" when an agent adds them via MCP,
"edited" when an agent changes them; a change by the user clears it. The new AgentBadge shows
"KI" / "KI geändert" in task rows, Kanban cards, the task detail, the inbox and lists.

Settings: export and import move out of "Webhooks, KI-Agenten & Export" into their own
category "Export & Import". Docs, help, README and changelog updated; v0.29.0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/domain/models.go

@@ -250,7 +250,7 @@ type Thought struct {
 	Content        string        `json:"content"`
 	Tags           []string      `json:"tags"`
 	Priority       string        `json:"priority"` // low | normal | high | urgent
-	Source         string        `json:"source"`   // manual | voice | webhook
+	Source         string        `json:"source"`   // manual | voice | webhook | agent
 	Status         ThoughtStatus `json:"status"`
 	IsCompleted    bool          `json:"isCompleted"`
 	ConvertedType  string        `json:"convertedType,omitempty"`  // task | document | list_item | document_block
@@ -268,6 +268,7 @@ type Thought struct {
 	SortOrder      int           `json:"sortOrder"`
 	CreatedAt      string        `json:"createdAt"`
 	TriagedAt      string        `json:"triagedAt,omitempty"`
+	AgentMark      string        `json:"agentMark,omitempty"` // created | edited: last change via MCP, untouched by the user since
 }
 
 type ThoughtReorderItem struct {
@@ -570,6 +571,7 @@ type ListItem struct {
 	SortOrder       int    `json:"sortOrder"`
 	CreatedAt       string `json:"createdAt"`
 	CompletedAt     string `json:"completedAt,omitempty"`
+	AgentMark       string `json:"agentMark,omitempty"` // created | edited: last change via MCP, untouched by the user since
 }
 
 type SharedList struct {