M12: Boards: a collaborative whiteboard file kind (#1229)

Board files (File > New board) with sticky notes, shapes with text, connectors that follow what they join (straight or elbow, arrowheads, labels), marker, highlighter and eraser, and stamps; a board toolbar and a contextual bar; the Design panel hidden on boards, Prototype and Dev Mode refused there. Boards are ordinary FigCraft files built from ordinary layers, so saving, undo, export, MCP and live sessions work unchanged. File tabs, recent files and Open files show a pen nib for design files and a note for boards (original icons drawn in code).

docs/mcp.md

@@ -330,6 +330,53 @@ tips; headless, it only sets the preference.
 {"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"export","arguments":{"format":"png","path":"dashboard.png"}}}
 ```
 
+### Boards
+
+A board is a file of its own kind for thinking together: `file.newBoard {name?}` opens one (its
+page is light; `inspect_document` says `kind: "board"`). Board objects are ordinary layers with a
+`board` entry `get_node` shows (`{type: sticky|shape|connector|label|stamp|ink, …}`), so the usual
+commands move, resize, recolour, copy, delete and undo them. On a design file the board commands
+refuse; on a board `proto.*`, `dev.*`, `view.prototype` and `view.devMode` refuse. Each of these is
+one undo step and returns the ids it made:
+
+- `board.sticky {x, y, text?, color?, author?, parent?}` → `{id, text}`: a sticky note (a square
+  frame whose height grows with its note; its text size shrinks as the note gets longer). `color`
+  is a board colour (`yellow orange red pink violet blue green gray`) or a hex colour; `author`
+  defaults to your name (`pref.userName`, or the one a live session gave you; `false` for none).
+- `board.nextSticky {id?, side?: right|below|left|above, edit?}` → `{id, text}`: a sticky of the
+  same colour beside the selected (or edited) one; with `edit: true` the app goes on typing in it
+  (`Shift+Cmd/Ctrl+Enter` in the app does both).
+- `board.shape {shape, x, y, width?, height?, text?, color?, parent?}` → `{id, text}`: a shape with centred,
+  wrapping text: `rectangle roundedRectangle ellipse diamond triangle speechBubble chevron`.
+- `board.connector {from, to, fromSide?, toSide?, style?: straight|elbow, startCap?, endCap?, label?}`
+  → `{id, label?}`: `from`/`to` are layer ids or `{x, y}` page points; sides are `auto` (the side
+  facing the other end) or `top right bottom left`; caps are stroke caps (default an arrow at the
+  end). The connector re-routes itself whenever what it joins moves or resizes, also when someone
+  else in a live session moves it; a deleted end stays where it was as a point. `board.label {id,
+  text}` sets its label (empty removes it).
+- `board.stamp {x, y, stamp: thumbsUp|heart|plusOne|star|question|check}` → `{id}`: a round badge
+  centred there, with your name on it for hover.
+- `board.ink {path | points, highlighter?, color?, select? (default true)}` → `{id}`: a marker (or
+  wide, see-through highlighter) stroke.
+- `board.setColor {ids?, color}`: stickies and shapes take it as their fill, connectors and ink as
+  their line. `board.setStyle {ids?, shape?, fontSize?, style?, startCap?, endCap?}`: a shape's
+  outline and text size, a connector's routing and arrowheads.
+- Tools for `pointer`: `tool.sticky {color?}`, `tool.shape {shape?}`, `tool.connector {style?}`
+  (drag from one object to another), `tool.marker {color?}`, `tool.highlighter {color?}`,
+  `tool.eraser` (drag over strokes), `tool.stamp {stamp?}`; Text and Section are the usual tools.
+
+```json
+{"command": "file.newBoard", "params": {"name": "Retro"}}
+{"command": "board.sticky", "params": {"x": 0, "y": 0, "text": "Went well", "color": "green"}}
+{"command": "board.sticky", "params": {"x": 240, "y": 0, "text": "To improve", "color": "pink"}}
+{"command": "board.connector", "params": {"from": 2, "to": 4, "style": "elbow", "label": "leads to"}}
+{"command": "board.stamp", "params": {"x": 200, "y": 0, "stamp": "plusOne"}}
+```
+
+`from` and `to` are the `id`s the two `board.sticky` calls returned (here `{"id": 2, "text": 3}` and
+`{"id": 4, "text": 5}` in a new board without an author name; a sticky with its author's name takes
+one more id). In a `batch`, step references (`{"from": {"$step": 1}, "to": {"$step": 2}}`, the `id`s steps 1 and 2 returned) avoid counting.
+
 ### Sections, handoff and arrow keys
 
 `run_command` with `object.wrapInSection {ids?, name?}` (Wrap in new section: layers on the page or
@@ -364,6 +411,10 @@ on; `key` resolves keys the way the canvas does. Commands behind keys:
 - `view.designPrototype` (`Shift+E`), `view.devMode` (`Shift+D`) and `view.leftSidebar`
   (`Shift+Cmd+\`) switch the right panel's tab or hide the left sidebar in the app (no-ops headless).
 - `doc.nextTab` / `doc.previousTab` (`Ctrl+Tab` / `Ctrl+Shift+Tab`): the next or previous open file.
+- Board tools (boards only): `tool.sticky` (`Q`), `tool.shape` (`B`), `tool.connector` (`X`),
+  `tool.marker` (`M`), `tool.highlighter` (`U`), `tool.eraser` (`E`), `tool.stamp` (`W`), and
+  `board.nextSticky` (`Shift+Cmd/Ctrl+Enter`, also while typing in a sticky). Keys no design-file
+  shortcut uses; on a design file they refuse.
 - `view.pan {dx, dy, big?}`: the arrow keys with nothing selected (`key ArrowRight` does the same)
   pan the view by 20 screen pixels a step, 200 with `big` (Shift).
 - `view.multiplayerCursors {on?}` (`Alt+Cmd+\`): show or hide others' cursors in a live session.