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/shell/manifest.yml

@@ -2,7 +2,10 @@
 ## /usr/bin with plain `dh $@` plumbing. Detection is not marker-based: the
 ## single-script heuristic of src/new/detect.rs (a lone *.sh or shebang
 ## file) maps here. The probe pre-filling the wizard answers from the
-## script file name lives in src/new/templates/shell.rs.
+## script file name lives in src/new/templates/shell.rs; everything else
+## is the data below (the skeleton script is executable, the install
+## mapping exists for skeletons only — packaging an existing tree leaves
+## the mapping to the user).
 ##
 ## Schema: see src/new/templates/mod.rs.
 
@@ -13,4 +16,10 @@ detect:
 build_depends: []
 architecture: all
 rules_dh_line: "dh $@"
-files: []
+files:
+  - path: "{command}.sh"
+    template: script.tpl
+    executable: true
+  - path: debian/install
+    template: install.tpl
+    skeleton_only: true