fix(resolver): treat type aliases as bare-TYPE authors in both gate directions [stdlib E1 attempt-4]

R4: a type alias is a `const_decl`, not a named-type decl, so the bare-TYPE
visibility gate ignored aliases — a namespaced-only alias leaked bare (silent
empty-struct stub, no diagnostic) and a flat-visible alias was poisoned by an
invisible same-name named type. Unify both type-author kinds (named type AND
alias) behind one per-module predicate `moduleTypeAuthor`, returning the author
KIND so resolution is decoupled from `findByName` timing (a forward/self
reference like `next: *ArenaChunk`, unregistered mid-registration, is still
recognised as an author and falls to the legacy stub instead of a false
"not visible"). The leak detector `nameAuthoredAsTypeAnywhere` now also scans
`type_aliases_by_source`. Single source of truth across named types, top-level
aliases, and parameterized/type-fn aliases — leak side and false-rejection side.

Behavior-preserving for single-author names (full suite byte-identical, paths
normalized). Generic / parameterized-protocol / Vector / type-function heads
stay legacy (0210). Block-local `Name :: <type>` remains a value const under the
reserved-name duality (pre-existing; the gate handles it safely, no leak).

Regressions: 0747 (ns-only alias bare -> not visible), 0748 (flat-visible alias
not poisoned by ns-only same-name struct). Both fail-before on 4bd57c8 /
pass-after here.

examples/expected/0747-modules-namespaced-only-bare-alias-not-visible.exit

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

examples/expected/0747-modules-namespaced-only-bare-alias-not-visible.stderr

@@ -0,0 +1,5 @@
+error: type 'Secret' is not visible; #import the module that declares it
+  --> examples/0747-modules-namespaced-only-bare-alias-not-visible.sx:14:9
+   |
+14 |     x : Secret = 7;
+   |         ^^^^^^

examples/expected/0747-modules-namespaced-only-bare-alias-not-visible.stdout

@@ -0,0 +1 @@
+

examples/expected/0748-modules-flat-alias-shadows-ns-only-type.exit

@@ -0,0 +1 @@
+42

examples/expected/0748-modules-flat-alias-shadows-ns-only-type.stderr

@@ -0,0 +1 @@
+

examples/expected/0748-modules-flat-alias-shadows-ns-only-type.stdout

@@ -0,0 +1 @@
+