fix(stdlib/E4): qualified generic alias head a.Box(..) selects the namespace author

The const-decl alias-registration path treated a qualified generic head
(`ABox :: a.Box(s64)`) only as a gate exemption, then read the bare last-wins
`struct_template_map` — so `ABox` and `BBox` both instantiated whichever
same-name template won globally (both size 16). attempt-9 routed the annotation
head sites through `qualifiedStructTemplate`; this applies the same selection to
the two alias-registration branches (.call and .parameterized_type_expr) before
the bare fallback, and extracts the shared instantiate-and-register logic into
`registerGenericStructAlias`.

ABox :: a.Box(s64) now resolves to a's template (size 8); BBox :: b.Box(s64) to
b's (size 16). Regression 0773 pins it (fail-before alias a=16 b=16, after a=8
b=16).

examples/0773-modules-qualified-generic-alias-author.sx

@@ -0,0 +1,28 @@
+// A type alias whose RHS is a qualified generic head `ns.Box(args)` must
+// instantiate the template AUTHORED by `ns`'s module — not the global same-name
+// template that won the last-wins `struct_template_map`. Two namespaces each
+// author a same-name generic `Box($T)` with a DIFFERENT layout (a: one field,
+// b: two fields). `ABox :: a.Box(s64)` and `BBox :: b.Box(s64)` must register
+// aliases over their OWN module's template (sizes 8 and 16) and stay DISTINCT,
+// so the field unique to b's layout (`y`) is reachable only through `BBox`.
+//
+// Regression (Phase E4): before the alias-registration path selected the
+// qualified author, the const-decl alias `.call` branch stripped the head to the
+// bare name and read the global `struct_template_map`, so `ABox` and `BBox` both
+// instantiated the last-wins template (both size 16). attempt-9 fixed the
+// annotation head sites; this pins the alias-registration sibling.
+
+#import "modules/std.sx";
+a :: #import "0773-modules-qualified-generic-alias-author/a.sx";
+b :: #import "0773-modules-qualified-generic-alias-author/b.sx";
+
+ABox :: a.Box(s64);
+BBox :: b.Box(s64);
+
+main :: () -> s32 {
+    ab : ABox = .{ x = 1 };
+    bb : BBox = .{ x = 10, y = 20 };
+    print("alias a={} b={}\n", size_of(ABox), size_of(BBox));
+    print("ab.x={} bb.x={} bb.y={}\n", ab.x, bb.x, bb.y);
+    0
+}

examples/0773-modules-qualified-generic-alias-author/a.sx

@@ -0,0 +1,2 @@
+// Author A's generic `Box` — one s64 field (size 8).
+Box :: struct($T: Type) { x: T; }

examples/0773-modules-qualified-generic-alias-author/b.sx

@@ -0,0 +1,3 @@
+// Author B's generic `Box` — two s64 fields (size 16). Same template NAME as
+// A's, different layout: the qualified alias head must select by namespace author.
+Box :: struct($T: Type) { x: T; y: T; }

examples/expected/0773-modules-qualified-generic-alias-author.exit

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

examples/expected/0773-modules-qualified-generic-alias-author.stderr

@@ -0,0 +1 @@
+

examples/expected/0773-modules-qualified-generic-alias-author.stdout

@@ -0,0 +1,2 @@
+alias a=8 b=16
+ab.x=1 bb.x=10 bb.y=20