infra: LaTeX preamble, theorem environments, tcolorbox, build system

Makefile

@@ -0,0 +1,37 @@
+# =============================================================================
+# Makefile — Differential Equations Handbook
+# =============================================================================
+
+TARGET = main
+TEX    = pdflatex
+BIBTEX = bibtex
+
+.PHONY: all quick clean view distclean
+
+## all: Full build (pdflatex -> bibtex if needed -> pdflatex x2)
+all:
+	$(TEX) -interaction=nonstopmode $(TARGET).tex
+	@if [ -f $(TARGET).blg ] || grep -ql '\\bibliography\|\\bibliographystyle' $(TARGET).tex; then \
+		$(BIBTEX) $(TARGET); \
+		$(TEX) -interaction=nonstopmode $(TARGET).tex; \
+		$(TEX) -interaction=nonstopmode $(TARGET).tex; \
+	fi
+
+## quick: Single pdflatex pass for rapid iteration
+quick:
+	$(TEX) -interaction=nonstopmode $(TARGET).tex
+
+## clean: Remove all auxiliary files
+clean:
+	rm -f $(TARGET).aux $(TARGET).log $(TARGET).out $(TARGET).toc \
+	      $(TARGET).lof $(TARGET).lot $(TARGET).nls $(TARGET).nlo \
+	      $(TARGET).vrb $(TARGET).synctex.gz $(TARGET).fls $(TARGET).out \
+	      $(TARGET).blg $(TARGET).bbl $(TARGET).run.xml
+
+## view: Open the resulting PDF
+view:
+	xdg-open $(TARGET).pdf
+
+## distclean: Clean + remove PDF
+distclean: clean
+	rm -f $(TARGET).pdf