Link View: every link of a component, drawn around it

Right-clicking a component now offers Link View alongside Properties, from
the wiresheet and from the navigation tree alike. It takes over the editor
pane the same way and answers one question -- what is wired to this
component, and where does it go.

The chosen component sits in the middle wearing the stroke a selected box
wears on the sheet, with what links into it on the left and what it links
out to on the right, so every arrow points the way the signal travels.
Pale yellow ground and no grid: nothing here can be positioned, because
the layout is derived from the links every time it is drawn and no part of
it is stored in the file. Read-only throughout -- no drag, no add, no
delete -- so a component's wiring can be read without the risk of
rearranging it.

Every line is grey, since this is not a wiresheet and a wire-blue line
would invite the reader to treat it as one. A link on the same sheet is
solid; one that crosses is dashed, keeps the grey knob that sheet paints
on the slot, and has the far component drawn in with its sheet named
beneath it. A reference the document cannot resolve gets a placeholder
naming the path, because a link the view silently dropped would be the one
thing a reader could not find out from here.

Clicking a wire or a component follows the link: it opens the sheet of the
end that is not the component the view is about, with the link selected in
red. A link that stays on one sheet therefore goes back to that sheet
where both ends are drawn, and one that crosses opens the other sheet --
the end the view could only show as a knob.

Supporting changes:

- draw_component_box is factored out of render_components, so the sheet
  and this view paint a component with the same code and a box cannot read
  differently between them. draw_knob takes its canvas for the same
  reason.
- The editor pane's hand-over is now shared: _take_editor_pane,
  _give_editor_pane_back and close_editor_panel replace the
  Properties-only versions, so "you have not saved that" is still asked
  once, in one place, whichever panel has the pane.
- Fixes the jump to a link's other sheet, which arrived with the link not
  selected. An after_idle callback is not late enough -- ttk dispatches
  its own selection event later than one of those, so the repaint wiped
  the selection. The link is left in _pending_link_selection for
  on_tree_select to honour once it has painted.
- Each gap is sized to hold a lane per wire crossing it, and lanes are
  handed out nearest-target-first, so a fan of a dozen links nests instead
  of crowding a dozen verticals into a 30px band.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app_state.py

@@ -8,7 +8,7 @@ so later rebinding would only ever be seen by the module that did it.
 import configparser
 import os
 
-VERSION = "0.0.0.054"
+VERSION = "0.0.0.055"
 PROPERTIES_FILE = os.path.join(os.path.dirname(os.path.abspath(__file__)), "editor.properties")
 DEFAULT_GRID_SIZE = 10
 DEFAULT_ADD_TIMESTAMP = True