[#21]:svarga:docs, refresh gallery (filled pie/donut + wireframe bar/histogram), nord dark theme

.gitignore

@@ -1,5 +1,6 @@
 # build
 /build/
+/build-*/
 /cmake-build-*/
 *.o
 *.a

doxy/Makefile

@@ -4,7 +4,16 @@
 DOXY    ?= doxygen
 OUT     = docs/doxygen/html
 
-.PHONY: all view clean
+# Gallery regeneration: dark renders use Nord (matched to the doxygen-awesome
+# dark page background #2b303b); light renders use Solarized Light (matches the
+# light page #fdf6e3). The default theme is selected at build time via the
+# -DPLOT_DEFAULT_THEME macro, so the example sources stay theme-neutral.
+DARK_THEME  ?= nord
+LIGHT_THEME ?= solarized_light
+EXAMPLES = line_chart scatter heatmap dashboard histogram bar density \
+           contour ohlc graph pie hexbin
+
+.PHONY: all view clean gallery
 
 all:
 	$(DOXY) Doxyfile 2>&1 | tee doxygen.log
@@ -19,5 +28,18 @@ all:
 view: all
 	xdg-open $(OUT)/index.html
 
+# Rebuild the theme-aware gallery SVGs from the example programs. Builds the
+# examples twice (dark + light default theme) and copies the renders into the
+# dark/ and light/ dirs that `all` ships into the published HTML.
+gallery:
+	cmake -S .. -B ../build-dark  -DPLOTS_BUILD_EXAMPLES=ON -DCMAKE_CXX_FLAGS=-DPLOT_DEFAULT_THEME=$(DARK_THEME)
+	cmake --build ../build-dark -j
+	cd ../build-dark/examples  && for e in $(EXAMPLES); do ./$$e; done
+	cp ../build-dark/examples/*.svg dark/
+	cmake -S .. -B ../build-light -DPLOTS_BUILD_EXAMPLES=ON -DCMAKE_CXX_FLAGS=-DPLOT_DEFAULT_THEME=$(LIGHT_THEME)
+	cmake --build ../build-light -j
+	cd ../build-light/examples && for e in $(EXAMPLES); do ./$$e; done
+	cp ../build-light/examples/*.svg light/
+
 clean:
 	$(RM) -rf docs/doxygen doxygen.log