Replace ASCII art with Unicode art

**Pages on which the enhancement should be made**
- [ ] interface-guide\docs\introduction\user-interaction.md (5)
- [ ] language-reference-guide\docs\system-functions\at.md (13)
- [ ] language-reference-guide\docs\system-functions\cr.md (2)
- [ ] language-reference-guide\docs\system-functions\na.md (6)
- [ ] language-reference-guide\docs\system-functions\nr.md (7)
- [ ] language-reference-guide\docs\system-functions\using.md (2)
- [ ] programming-reference-guide\docs\component-files\component-files.md (13)
- [ ] programming-reference-guide\docs\component-files\internal-structure.md (25)
- [ ] programming-reference-guide\docs\component-files\the-effect-of-buffering.md (3)
- [ ] programming-reference-guide\docs\defined-functions-and-operators\dfns-and-dops\recursion.md (8)
- [ ] programming-reference-guide\docs\defined-functions-and-operators\traditional-functions-and-operators\control-structures\control-structures-summary.md (1 hit)
- [ ] programming-reference-guide\docs\defined-functions-and-operators\traditional-functions-and-operators\control-structures\if-statement-definition.md (3)
- [ ] programming-reference-guide\docs\defined-functions-and-operators\traditional-functions-and-operators\control-structures\repeat-statement-definition.md (2)
- [ ] programming-reference-guide\docs\defined-functions-and-operators\traditional-functions-and-operators\control-structures\select-statement-definition.md (2)
- [ ] programming-reference-guide\docs\defined-functions-and-operators\traditional-functions-and-operators\control-structures\trap-statement-definition.md (1 hit)
- [ ] programming-reference-guide\docs\defined-functions-and-operators\traditional-functions-and-operators\control-structures\while-statement-definition.md (3)
- [ ] programming-reference-guide\docs\error-trapping\error-trapping-examples.md (2)
- [ ] programming-reference-guide\docs\object-oriented-programming\class-members\properties\keyed-properties-print.md (8)
- [ ] programming-reference-guide\docs\object-oriented-programming\class-members\properties\keyed-properties\keyed-property-example-one.md (8)
- [ ] programming-reference-guide\docs\object-oriented-programming\constructors\empty-arrays-of-instances-how.md (7)

**Describe the enhancement you would like**
Replace ASCII art with Unicode art, e.g.:
```
DISPLAY F.Event
.⊖------------.
| .→--------. |
| | .⊖. .⊖. | |
| | | | | | | |
| | '-' '-' | |
| '∊--------' |
.∊------------.
```
becomes
```
]Display F.Event
┌⊖────────────┐
│ ┌→────────┐ │
│ │ ┌⊖┐ ┌⊖┐ │ │
│ │ │0│ │0│ │ │
│ │ └~┘ └~┘ │ │
│ └∊────────┘ │
└∊────────────┘
```
and
```
.-. .-. .-.
|1| |2| |3|
.-----.-----.-------.
| One | Two | Three |
--------------------.
```
becomes
```
┌─┐ ┌─┐ ┌─┐
│1│ │2│ │3│
├─┴───┼─┴───┼─┴─────┐
│ One │ Two │ Three │
└─────┴─────┴───────┘
```

**Additional information**
Note also the replacement of the `DISPLAY` utility function with the `]Display` user command.

Start by searching the listed Markdown files for the ASCII diagrams and DISPLAY references, using the issue checklist to track all 19 paths. Compare each diagram with the Unicode examples in the issue and confirm the rendered documentation preserves the intended layout; done means every listed hit is updated and DISPLAY is described as ]Display.

Written by the indexing model from the issue text.