Browse: show "No Icon" for elements that have no icon of their own

[ctgnz]

An entity that has no icon of its own still renders its frame, so Browse shows an empty frame next to the
label. That reads as an icon that failed to load rather than an element that legitimately has nothing to
draw. It should say something instead - generic No Icon text is enough.

What it looks like now

/Common/symbol/entity/UNSPECIFIED?trim=true returns a well-formed 200 with the frame ellipse and no icon
content:

<svg:svg ... viewBox="156.50 246.50 299.00 299.00">
  <svg:title>Unspecified</svg:title>
  <svg:g id="frame_1_">
    <svg:ellipse id="Group" cx="306.0" cy="396.0" rx="144.0" ry="144.0" fill="#80E0FF" .../>
  </svg:g>
</svg:svg>

Nothing is broken - there is simply no icon layer. Compare UNKNOWN, which carries the ?.

How to detect it

These elements are marked GraphicType.NA in the model, e.g. in CommonEntity:

UNSPECIFIED("00", "Unspecified", GraphicType.NA),
UNKNOWN("01", "Unknown Symbol", GraphicType.MAIN),

There are 109 GraphicType.NA elements across the generated jmsfx-standard, spread over most symbol
sets, so this is not an edge case. Many are grouping nodes whose children carry the actual icons, which is
precisely where an empty frame is most confusing.

MainElement already has isFreeCanvas() / isFullFrameIcon() predicates in this shape, so a matching
isNoIcon() (or similar) would be the natural place to expose it to the template, rather than having
entity-list.html compare the enum directly.

Scope

Browse (entity-list.html) is where it was noticed. Worth checking whether Generate shows the same empty
frame for these elements and wants the same treatment.

[ctgnz]

Revisited while implementing this, and the premise was wrong for most of the tree.

For a symbol set that draws a frame, an empty frame is the right answer. The frame itself carries
information - standard identity, status, dimension - so an element with no icon of its own is not showing
"nothing", it is showing everything it has. Replacing that with a "No Icon" label would discard real
content in order to explain an absence that is not really there.

A first pass did exactly that, at all five places a main icon appears, and the effect on Land Units made
the point: seven of its eleven top-level entities are hierarchy nodes, so most of the column turned into
placeholders where there had been perfectly good frames. Reverted, and #87 carries only #69.

What is actually odd

Control Measure, which draws no frame at all. An element with no graphic there really does render
nothing, and it looks broken rather than empty. It is also the set where it matters least: exactly one
entity supplies a real graphic, so the oddity is nearly uniform across the set - possibly something to
live with rather than fix.

The idea worth keeping

Rather than replacing the icon, use the AA amplifier to display something like {No Icon} within
the frame. That keeps the frame and everything it says, and adds the explanation rather than substituting
for it - which is the distinction the first attempt got wrong. It would also apply uniformly, framed or
not.

Back on the backlog rather than in 1.5.0, since it now needs a design decision rather than a template
change.