Let the agent copy nodes, also into another graph (#434)

The agent built every part again that already stood in a graph,
node by node, while the editor has Ctrl+C and Ctrl+V for it. The new
command `copy_nodes` in the area graphs copies nodes into the same
graph or another one, in one undo step with the rest of the call.

- The links between the copied nodes come along, and so do groups
  and comments that are only about copied nodes. A node belongs to a
  group by its middle, as when it is dragged. `boxesAbout` in
  annotationFollow.ts decides this.
- `made` names each copy by the id of its original, so later steps
  link to it with `$copy.<id>`. `$copy` alone is the first one.
- Without x and y the copies are arranged at the end of the call like
  new nodes. With them they keep their layout, top left corner there.
- Nodes the target graph does not take are refused by name, not left
  out as Ctrl+V does. The rule is the graph tab's: `fitsGraph` and
  `fittingPart` moved from clipboard.ts to paletteEntries.ts.
- A copied Variables node takes the variables of its behavior along
  into the target behavior (`CarryVariablesCommand`), with default,
  value, Keep and Private. A variable of that name of another kind
  there is refused.
- The relay's instructions name `copy_nodes`.

Found on the way:
- Groups made by the agent can take in a node of another group once
  the nodes are arranged. lint_graph does not count that.
- Undo after a paste leaves an empty `groups: []`, as
  AddAnnotationCommand does. It is the same as no list.

Tests:
- agent-copy (new, 3 tests) with the agent, relay, clipboard and
  palette tests: 118/118.
- Counter-probes: 6 bendings, all compile, all red.
- e2e 71 (atx): ALL PASSED, 26 checks.
- Gate (atx): CHECK EXIT 0, 327 files, 5024 tests.
- Live in the MCP Test Project: 5 nodes of Arrow keys walk into a new
  behavior, 6 links, group, comment and speed (300) along, lint_graph
  0 everywhere, taken back with undo.

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

tools/mcp/relay.mjs

@@ -45,9 +45,11 @@ const INSTRUCTIONS = [
   'over a long link. Check with lint_graph, the crossings too: when there are more than the links',
   'need, arrange_graph orders the whole graph for the fewest. Put nodes that belong together into a',
   'group with add_group, and say what they do with add_comment; a comment a node lies on',
-  '(coveredNotes) goes back above its nodes with fit_group. Music plays nothing without an',
-  'instrument, and an instrument sounds only the notes its Notes nodes take in, C4 to B4 in a new',
-  'one: get_asset lists under silent what of a pattern, song or composition is not heard.',
+  '(coveredNotes) goes back above its nodes with fit_group. A part already built elsewhere is',
+  'copied with copy_nodes, into the same graph or another, rather than built again. Music plays',
+  'nothing without an instrument, and an instrument sounds only the notes its Notes nodes take',
+  'in, C4 to B4 in a new one: get_asset lists under silent what of a pattern, song or composition',
+  'is not heard.',
   'apply_preset gives an instrument that sounds every note in one step. Pictures, fonts, sounds',
   'and videos are files: list_files lists those the server holds, add_file_asset makes an asset',
   'of one. Before deleting or reworking an asset, get_asset says under usedBy what names it.',