Let the agent edit animations, frames, tiles and tilemaps (#429)

After stage 5a the agent could build behaviors and scenes, but not
animate an object, cut a texture into frames or paint a tilemap.
Stage 5b adds three areas with 30 commands, 115 in all.

- animation (12): set the root, add, retarget and make rows relative,
  set, move, copy and delete keys, easing, insert or remove frames,
  and curve points.
- textures (8): add, change and delete frames, slice a grid, nine
  slice, sorting line and collision outline.
- tiles (10): the images of a tile, painting tilemaps, layers (add,
  copy, move, change) and the border of a placed tilemap.
- get_asset names the targets of an animation with their animatable
  properties. A tilemap up to 400 cells shows its cells, a bigger one
  only their count.
- After such a call the editor opens the tab of the animation, curve,
  texture, tile or tilemap. A frame edit selects the frame there.
- One paint step takes rectangles and single cells. Rectangles go
  first, so a cell can cut a hole into a rectangle. Cells outside the
  grid, ids that are no tile and more than 20 000 cells are refused.
  The grid is the tilemap's largest, a grown placement included.

Left out on purpose: Generate collision, because it reads the pixels
of the texture, and pasting keys, which goes through the clipboard.

Found on the way:
- Nine slice without fill now keeps the fill the image has. The
  model's default is repeat, not stretch as first described.
- Painting ran the other way round, rectangles overwrote cells.

Tests:
- agent-art (new, 11) and the other agent tests green, 64/64.
  5 bends of the code, all red.
- e2e 71 on atx: 23/23, the new check opens the agent's animation in
  its tab and reads its targets.
- Gate on atx: 321 files, 4969 tests.
- Live on a test project: a Spin animation of 360 degrees in 30
  frames matched 12 degrees per frame to 0.01 frames in the game.

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

src/editor/agent/tools.json

@@ -44,7 +44,7 @@
   {
     "name": "get_asset",
     "title": "Read an asset",
-    "description": "One asset as stored: its property values, the rows of its properties (key, kind, default), the objects of a scene or container with their names and positions (the content of a placed container too, marked fromContainer). A graph is only counted here; read it with get_graph.",
+    "description": "One asset as stored: its property values, the rows of its properties (key, kind, default), the objects of a scene or container with their names and positions (the content of a placed container too, marked fromContainer), what the rows of an animation may aim at (targets), the cells of a small tilemap. A graph is only counted here; read it with get_graph.",
     "inputSchema": {
       "type": "object",
       "properties": { "asset": { "type": "string", "description": "Id of the asset." } },