[Icons] Add a badge icon treatment

Restore the filled-disc look the ready/not-ready icons had before the
one-glyph cutover, without bringing back palette-locked art.

IconStyle::Badge composes the existing sentinel SVG at paint time: a
gradient disc, a dark ring, and the glyph re-weighted and inked for
contrast against the tone. Line stays the default and is unchanged.

Only the two state icons opt in. The add/remove icons keep the line
treatment because their old art was a filled glyph with an outline and
no disc, so badging them would invent a look the UI never had. Disabled
badges fall back to the line glyph so an unavailable control still reads
as unavailable.

oracle/CMakeLists.txt

@@ -32,6 +32,7 @@ set(oracle_SOURCES
     ../cockatrice/src/interface/pixel_map_generator.cpp
     ../cockatrice/src/interface/theme_config.cpp
     ../cockatrice/src/interface/theme_icon.cpp
+    ../cockatrice/src/interface/theme_icon_badge.cpp
     ../cockatrice/src/interface/theme_manager.cpp
     ${VERSION_STRING_CPP}
 )