Tasks API: Extend POST /tasks #955

Extend create endpoint.

Base path: /api/v2/organizations/{org}/members/{user}

Behavior

• Body: { name?, template_id? | recipe_id?, parameters?: { [k]: string }, input?: string }
• Require one of template_id or recipe_id.
• Recipe-based creation.

Request model

• name?: string
• template_id?: uuid
• recipe_id?: uuid
• parameters?: map[string]string

Response model (task)

• template_id: uuid
• recipe_id?: uuid (post-MVP)
• created_at, updated_at, started_at?, completed_at?
• last_error?: string

Depends on: #898