new: port the shell, empty, makefile and go templates to manifests

Move the four templates' static file bodies into .tpl files under
data/templates/<id>/, referenced by their manifests' files: lists —
the shell skeleton script (executable, {command}-named) with its
skeleton-only debian/install mapping, the empty template's stub README,
the makefile hello.c/Makefile skeleton with its skeleton-only install
mapping, and go's go.mod/main.go skeleton (the go directive of go.mod
stays a literal: nothing about it is answer-derived).

The empty template ends up hookless — zero Rust, its registry entry
points at no hooks — and src/new/templates/empty.rs is deleted. The
shell and go hooks shrink to their probes (plus go's {go_import_path}
context value); the makefile hooks keep only the existing-tree hint
probing the packaged Makefile for a phony install: target, since that
heuristic reads the tree and cannot be data.

data/templates/makefile/install.tpl

@@ -0,0 +1 @@
+{command} usr/bin/{command}