Add the board, and finish v1.1 (stage 9e)

The board is the user's design: the document as lists and blocks, the
way Scratch nests blocks inside a loop. Each node without a parent (the
root, then each loose node) is a column with its title in the top border;
its children are cards in it, one under the other; a card with children
on show wraps them in a C: a joint at its bottom left, a bracket down the
left two cells further in, and a foot closing it. Blocks nest as deep as
the tree does. The columns by tag or color the first design had are
dropped (the user's pick), and :board takes no arguments any more.

j and k go down and up a column in reading order, into the blocks; h and
l go to the column beside, onto the card nearest the cursor's height.
Titles are typed right in their cards, and visual mode selects in
reading order as the outline does. <Space>vb or :board shows it.

Move mode (M, the user's pick) moves the card through the tree: h and l
to the end of the column beside, j and k past the cards around it, into
an open block and out of one at its end. A column's own node trades
places with the loose column beside it; the root's column stays first.
A drag does the same with the mouse: dropped on a card it goes after it,
on a block's card into it, on a column at its end.

The fallback message for a key a view ignores now names the view ("does
nothing in the board view"). The version goes to 1.1.0: stage 9 is done.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

README.md

@@ -4,8 +4,8 @@ Brainstorm in the terminal: ideas as nodes on a 2D canvas, connected, folded
 and color-coded, across as many documents as you like. Vim keys first; the
 mouse works too. Runs on Windows and Linux.
 
-> **Status:** v1 is built: everything on [DESIGN.md](DESIGN.md)'s v1 list.
-> v1.1 (the board, a search across documents, tidying, export) comes next.
+> **Status:** v1.1 is built: everything on [DESIGN.md](DESIGN.md)'s v1 and
+> v1.1 lists. What comes later is listed there too.
 
 ## Build and run
 
@@ -99,7 +99,8 @@ The plan for the everyday keys (all of them are in DESIGN.md):
 | `<Space>p`        | a portal to another document (`:portal file`, or a new document's title) |
 | `<Space>o`        | this branch out, into a document of its own, with a portal in its place (`:branchout`) |
 | Enter or `gf` `gu` | through a portal / up to the portals that lead here |
-| `<Space>`         | the action menu: `c` color, `t` tags, `b` documents, `i` inbox, `vo` outline, `vn` note… |
+| `<Space>`         | the action menu: `c` color, `t` tags, `b` documents, `i` inbox, `vo` outline, `vn` note, `vb` board… |
+| board             | `<Space>vb` or `:board`: a column per node without a parent, its children as cards, a card with children wrapping them as Scratch's loop blocks do; `j` `k` cards, `h` `l` columns, `M` then `hjkl` (or a drag) moves a card |
 | `Ctrl-w v` `Ctrl-w s` | split the pane side by side / stacked (`Ctrl-w hjkl` to move between them) |
 | `gt` `gT`         | the next / previous document                       |
 | `:` `?`           | command line, help (search it with `/`, Enter runs the key or command) |