build: add release/debug profiles (-O2 / -g2)

Makefile.am

@@ -13,3 +13,25 @@ EXTRA_DIST = tests/run.sh scripts/build-static.sh
 .PHONY: static
 static:
 	$(SHELL) "$(srcdir)/scripts/build-static.sh"
+
+# Release/debug build profiles (explicit opt-in; `make` alone is unchanged).
+#
+# Mechanism: CFLAGS is passed on the recursive make COMMAND LINE. Automake's
+# compile rule ends with `$(AM_CFLAGS) $(CFLAGS)`, so a command-line CFLAGS
+# overrides configure's `-g -O2` default while AM_CFLAGS (-std=c23 -Wall
+# -Wextra -Wpedantic) is always kept. No configure.ac churn, no default
+# build impact. Both targets clean first so a previous profile's objects
+# can never be reused as a fresh build.
+#
+# release: -O2 -DNDEBUG, no -g, then the binary is stripped (needs binutils
+#          `strip` on PATH).
+# debug:   -g2 only, no -O/-O2, no NDEBUG (default CFLAGS are overridden).
+.PHONY: release debug
+release:
+	$(MAKE) clean
+	$(MAKE) CFLAGS="-O2 -DNDEBUG"
+	strip src/stupidtools
+
+debug:
+	$(MAKE) clean
+	$(MAKE) CFLAGS="-g2"