feat: add initial project scaffolding with Makefile, C sources, web UI, and documentation

Add Makefile with build targets for sudoku solver, generator, and coverage reporting.
Include NOTES.md explaining sudoku difficulty factors and solving techniques.
Add README.md with puzzle examples and generator output.
Implement app.js with Grid and Grid2 classes for rendering puzzle data in the browser.
Add box.c with functions for box indexing, grid-to-array conversion, and box value extraction.
Include footer.h with terminal size detection, cursor positioning, and footer display utilities.
Add index.html with CSS grid layout and script loading for the web interface.
Include rlib.h as a large utility header library.

Makefile

@@ -0,0 +1,30 @@
+all: build_and_run
+
+build_and_run:
+	gcc sudoku.c -o sudoku -Wall -Wextra 
+	./sudoku
+
+gen1:
+	gcc sudoku_gen1.c -o sudoku_gen1 -Wall -Wextra -Ofast
+	./sudoku_gen1
+
+solve: solve.c rlib.h
+	gcc solve.c -Ofast -o solve
+	$(MAKE) solve_auto
+
+solve_manual:
+	./solve 
+
+solve_auto:
+	./solve auto
+
+coverage:
+	gcc -pg -fprofile-arcs -ftest-coverage -g -o sudoku sudoku2.c
+	./sudoku
+	lcov --capture --directory . --output-file sudoku.coverage.info
+	genhtml sudoku.coverage.info --output-directory sudoku.coverage
+	@rm -f *.gcda   2>/dev/null
+	@rm -f *.gcno   2>/dev/null
+	@rm -f sudoku.coverage.info 2>/dev/null
+	@rm -f gmon.out 2>/dev/null
+	google-chrome sudoku.coverage/index.html