Makefile: tidy kind, operator-sdk, and opm fetch rules

[frobware]

While working on #528 I noticed three things in the Makefile's tool-fetching rules that compounded each other. LOCALBIN ?= $(shell pwd)/bin made $(KIND) and $(OPERATOR_SDK) reachable only by absolute path -- make bin/kind failed with "no rule for target", and the .PHONY: kind / .PHONY: operator-sdk aliases existed only to give those targets a typeable name. Regular prerequisites on $(LOCALBIN) meant Make considered the binaries stale whenever the directory's mtime moved; the test -s guards inside the recipes were the only thing stopping an actual redownload. And curl -Lo without -f writes HTTP error bodies straight to the output path, so a 404 leaves a non-empty file the next run treats as already installed.

First commit switches LOCALBIN to a relative path, drops the .PHONY aliases (their job is now done by typing the file target directly), and updates the dependents (load-images-kind, setup-kind, setup-kind-registry, destroy-kind, bundle, bundle-deploy, bundle-deploy-openshift, bundle-undeploy) to depend on $(KIND) / $(OPERATOR_SDK) instead of the dropped aliases. The one consumer that still needs an absolute path is setup-envtest --bin-dir, because its output becomes KUBEBUILDER_ASSETS for per-package test binaries whose cwd changes; that single call site is wrapped with $(abspath $(LOCALBIN)).

Second commit switches both download rules to an order-only prerequisite on $(LOCALBIN) (so directory mtime no longer triggers rebuilds) and reshapes the recipes around curl -fLo $@.tmp followed by mv $@.tmp $@. The -f makes curl exit non-zero on HTTP errors, the rename keeps the canonical $@ path absent until the full chain succeeds, and the test -s guards become redundant.

Third commit applies the same pattern to the opm rule, which was the most tangled of the three: a .PHONY: opm target whose recipe body was wrapped in nested ifeq blocks, plus a mid-rule reassignment where OPM = ./bin/opm was overwritten inside the else branch with OPM = $(shell which opm) -- so $(OPM) silently became whatever version happened to be in $PATH if the local download was missing, pinning v1.45.0 in the URL while accepting whatever opm the user had installed. The rule now matches $(KIND) and $(OPERATOR_SDK) exactly: an $(OPM) file target with order-only $(LOCALBIN) prereq, atomic download, and OPM_VERSION lifted to the Tool Versions block alongside KIND_VERSION and OPERATOR_SDK_VERSION. catalog-build depends on $(OPM) directly. The system-opm fallback is dropped: override OPM on the command line if you want to point at something specific.

Test plan

• make help no longer lists the bare kind, operator-sdk, or opm aliases
• make bin/kind, make bin/operator-sdk, make bin/opm trigger their download recipes
• make test runs with KUBEBUILDER_ASSETS resolved as an absolute path
• make setup-kind, make bundle-deploy, make catalog-build etc. fire their tool prereqs

[frobware]

cc @alebedev87