Add connect mode, portals, backlinks and renames (stage 8d, v1)

Part 8d, the last of stage 8, and with it everything on DESIGN.md's v1
list.

Connect mode (C): the cursor goes to another node, a dashed arrow in the
visual color follows it, and Enter links the two; then the cursor goes
back to where C was typed (the user's pick). d removes the line between
them (a branch is cut, and the child comes loose), > puts the node under
the other one, and <Space> a, l, c, s and t style the line as you watch,
making it when it isn't there yet. Everything connect mode changes is one
undo group, and Esc takes it back with History::cancel, which leaves
nothing to redo. From visual mode every selected node connects, and the
line pickers go back to connect mode when they close.

Portals show their document live, from a cache of what each document
file holds (open documents from their buffers, the others from their
files, looked at every second): the root's title, its color and how many
nodes it has, or ? when the document isn't there. Enter or gf goes
through, as a jump, and the pane's breadcrumb starts with the documents
it came through. <Space>p types :portal (the user's pick): a path as :e
takes it, or the title of a new document. Backlinks are put right
whenever a document is opened or saved; the root shows how many, the
Note view lists them, gu goes up to them (the user's pick) and
:backlinks lists them.

File names follow the root's title: when it changed, the next save
renames the file (-2 when the name is taken; a folder's default document
keeps its name), and the portals pointing at it, its backlinks in the
documents it leads to, the recent documents, the capital marks and the
jump lists follow. A portal whose file was moved by hand finds its
document in that folder by uid. Portals in a register keep full paths,
so a pasted portal leads to the same document from any folder.

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

src/app/text_edit/tests.rs

@@ -1,9 +1,12 @@
 //! Editing a node's text: rapid entry, empty titles, `o` inside a title,
 //! bodies and tags, and the document following the text.
 
+use std::path::Path;
+
 use super::*;
 use crate::app::buffer::Buffer;
 use crate::app::mode::Mode;
+use crate::app::portals::Portals;
 use crate::input::bindings::Context;
 use crate::input::engine::{KeyEngine, Outcome};
 use crate::input::key::parse_keys;
@@ -46,12 +49,15 @@ impl App {
     fn press(&mut self, keys: &str) {
         for key in parse_keys(keys, DEFAULT_LEADER).unwrap() {
             let normal = Mode::Normal;
+            let portals = Portals::default();
             let ctx = ViewContext {
                 doc: self.buffer.doc(),
                 cursor: self.buffer.cursor(),
                 mode: &normal,
                 theme: &self.theme,
                 settings: &self.settings,
+                portals: &portals,
+                folder: Path::new("."),
             };
             let actions = match &mut self.mode {
                 Mode::Text(edit) if edit.editor.is_typing() => {
@@ -79,12 +85,15 @@ impl App {
                 }
                 Action::App(AppAction::StartEdit(start)) => {
                     let normal = Mode::Normal;
+                    let portals = Portals::default();
                     let ctx = ViewContext {
                         doc: self.buffer.doc(),
                         cursor: self.buffer.cursor(),
                         mode: &normal,
                         theme: &self.theme,
                         settings: &self.settings,
+                        portals: &portals,
+                        folder: Path::new("."),
                     };
                     match TextEdit::start(&ctx, start) {
                         Ok(edit) => self.mode = Mode::Text(edit),