Properties: a hidden-slots toggle, and bools filled by their state

@hidden is now filtered by default. niagara.html says hidden slots "are
designed to be invisible to the user" and that interfaces should rarely
display them; every one under Sedona home is a void action a kit uses
internally, such as HdwAI.checkType. A "Hidden slots (n)" checkbox in the
footer brings them back and the answer sticks for the session. The checkbox
only appears on a type that has some, and the rows are always built -- the
toggle grid_removes and re-grids them, so an emptied grid row collapses rather
than leaving a gap.

A bool now says which state it is in by the colour of its field rather than by
a dot beside it that had to be learnt: green true, red false, blue null, with
the words left black so they read as easily as every other value. Dropping the
dot also lets a bool's field line up with the numbers above and below it.

Two things that needed changing to get there:

  - a dropdown is offered only where there is a choice to make. A read-only
    bool or enum gets a plain field, since a disabled dropdown is an arrow
    that does nothing -- and a read-only bool is still filled, because a
    runtime bool has a state too.
  - the dropdown is a tk.OptionMenu, not a ttk.Combobox. On the Windows themes
    a Combobox draws its field with a native element and ignores
    fieldbackground outright, so a bool could never be filled with its colour.

An OptionMenu reports through its variable rather than an event, which means
loading a row looks exactly like choosing one -- so the load is flagged and the
unsaved-state tint left alone until every row is in, or the view would open
already claiming edits nobody made.

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 = "0.0.0.048"
+VERSION = "0.0.0.051"
 PROPERTIES_FILE = os.path.join(os.path.dirname(os.path.abspath(__file__)), "editor.properties")
 DEFAULT_GRID_SIZE = 10
 DEFAULT_ADD_TIMESTAMP = True