[rhannequin]

Adds names to the map:

chart.render(
  Skymap::Layers::ConstellationLines.new(lines: lines, stars: stars),
  Skymap::Layers::ConstellationNames.new(lines: lines, stars: stars),
  Skymap::Layers::Stars.new(stars: stars),
  Skymap::Layers::Planets.new(ephem: ephem, labels: true)
)

• ConstellationNames writes each name in the middle of the biggest part of the constellation that is above the horizon, so a figure in several parts such as Serpens is named on one of its parts. A constellation is left out when half of its stars or more are below the horizon, or when it has no lines (Mensa and Microscopium)
• Planets writes the name of each planet next to it with labels: true, on the side of the center of the map so it stays inside the sky. It is off by default, and names: changes the names
• The names come from a new data/constellations/iau/names.csv. Astronoby has names too, but it keeps only the first word of the names with several words ("Ursa Minor" becomes "Ursa") and fails to read "Boötes" when the locale is ASCII
• names: takes anything that gives a name from an abbreviation, such as a hash, so the names can be translated. A constellation without a name is left out
• Both kinds of names are drawn with a new Renderer::Caption, which has a color for each kind

The map of the README shows the names. The Moon is drawn after them there and covers Aquarius, which is only a matter of layer order.

[Copilot]

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What changed in this PR

Adds constellation names and optional planet labels to Skymap’s layered SVG rendering, with customizable constellation names for translation.

Changes:

• Adds a UTF-8 catalog of all 88 constellation names and a layer that labels constellations when more than half their supplied stars are above the horizon.
• Introduces shared caption rendering with distinct colors for constellation and planet names.
• Adds tests, documents the new options, and updates the example map.

File	Description
spec/​skymap/​renderer/​svg_spec.rb	Tests caption positioning, sizing, and colors.
spec/​skymap/​layers/​planets_spec.rb	Tests default behavior and optional planet labels.
spec/​skymap/​layers/​constellation_names_spec.rb	Tests visibility, placement, scaling, and custom names.
spec/​skymap/​catalog/​constellation_names_spec.rb	Tests name lookup, accents, and catalog completeness.
sky_map.svg	Adds constellation and planet names to the example map.
README.md	Documents naming layers, options, and catalog data.
lib/​skymap/​renderer/​svg.rb	Renders captions using shared text drawing and kind-specific colors.
lib/​skymap/​renderer/​caption.rb	Defines the caption rendering data type.
lib/​skymap/​layers/​planets.rb	Adds optional names beneath visible planets.
lib/​skymap/​layers/​constellation_names.rb	Places constellation names among their visible stars.
lib/​skymap/​catalog/​constellation_names.rb	Loads UTF-8 names and supports abbreviation lookup.
lib/​skymap.rb	Loads the new catalog, layer, and caption type.
data/​constellations/​iau/​names.csv	Supplies names for all 88 IAU constellations.
CHANGELOG.md	Records constellation naming and optional planet labels.

_{Review effort: Balanced}