fix(build): resolve mise via PATH instead of hardcoded ~/.local/bin path

mise now lives at /opt/homebrew/bin/mise (Homebrew install), so the
hardcoded MISE_BIN default broke make test/deps/compile. Fall back to
PATH lookup, matching what the check target already did.

app/Makefile

@@ -1,6 +1,6 @@
 # Makefile for Firehose app
 
-MISE_BIN ?= $(HOME)/.local/bin/mise
+MISE_BIN ?= mise
 MISE_EXEC = $(MISE_BIN) exec --
 
 .PHONY: check precommit deps compile test format credo

blogex/Makefile

@@ -1,6 +1,6 @@
 # Makefile for Blogex library
 
-MISE_BIN ?= $(HOME)/.local/bin/mise
+MISE_BIN ?= mise
 MISE_EXEC = $(MISE_BIN) exec --
 
 .PHONY: test format