fix(stdlib/E4): type-fn head gate selects the TYPE-FUNCTION author (ordinary fn must not vouch)

attempt-7 made the type-fn head gate kind-aware (a non-function no longer
vouches), but it still accepted ANY function author: a directly-visible
ORDINARY function (`Make :: () -> s32`, zero `$`-params) authorized a hidden
2-flat-hop type-function head (`Make :: ($T) -> Type`), so `size_of(Make(s64))`
silently instantiated the 2-hop type-fn and printed `size=8` at exit 0.

Narrow the author view from "any fn_decl" to "a TYPE-FUNCTION" via a new
`typeFnAuthor` predicate (`fnDeclOfRaw` + `type_params.len > 0`), the same
discriminator every instantiation site uses to recognize a type-fn head. Both
`flatFnAuthorVisible` and `flatFnAuthorAmbiguous` now count only type-fn
authors, so a same-name ordinary function — which cannot be the type head being
instantiated — does not vouch for a 2-hop type-fn head.

Regression 0771: main -> b (`Make :: () -> s32` ordinary fn + flat-imports c)
-> c (`Make :: ($T) -> Type`); `size_of(Make(s64))` -> "type 'Make' is not
visible", exit 1 (fail-before on 94c3cd7: size=8 exit 0). 0770 (non-fn vouch),
0769 (type-fn ambiguity), 0768/0767/0766-0763, 0208/0210 (valid type-fn heads),
0544/0706/0105 and FFI all green & byte-identical.

examples/expected/0771-modules-type-fn-head-ordinary-fn-no-vouch.exit

@@ -0,0 +1 @@
+1

examples/expected/0771-modules-type-fn-head-ordinary-fn-no-vouch.stderr

@@ -0,0 +1,5 @@
+error: type 'Make' is not visible; #import the module that declares it
+  --> examples/0771-modules-type-fn-head-ordinary-fn-no-vouch.sx:23:32
+   |
+23 |     print("size={}\n", size_of(Make(s64)));
+   |                                ^^^^

examples/expected/0771-modules-type-fn-head-ordinary-fn-no-vouch.stdout

@@ -0,0 +1 @@
+