Rework Makefile with install/link/update targets and auto-generation

Add gen-update-targets.sh to parse flake.nix and generate grouped
update targets (update-kyle, update-mc). Makefile now has install
(copy) and link (symlink) targets for rebuild-nixos. Also fix mc
flake input URLs to use /mc/ org path.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Makefile

@@ -1,12 +1,18 @@
 BIN_DIR :=	${HOME}/.local/bin
-SCRIPTS :=	$(BIN_DIR)/rebuild-nixos
 
-.PHONY: all
-all: $(SCRIPTS)
+.PHONY: install link update-targets
+
+install: $(BIN_DIR)
+	cp script/rebuild-nixos $(BIN_DIR)/
+	chmod +x $(BIN_DIR)/rebuild-nixos
+
+link: $(BIN_DIR)
+	ln -sf $(CURDIR)/script/rebuild-nixos $(BIN_DIR)/
 
 $(BIN_DIR):
 	mkdir -p $(BIN_DIR)
 
-$(BIN_DIR)/rebuild-nixos: script/rebuild-nixos
-	cp script/rebuild-nixos $(BIN_DIR)/
-	chmod +x $(BIN_DIR)/rebuild-nixos
+update-targets.mk: flake.nix script/gen-update-targets.sh
+	script/gen-update-targets.sh > $@
+
+-include update-targets.mk