lang: fn aliases dispatch like their target (fix 0121) — scan-time registration through the shared alias-chain walk

Renamed fn aliases failed for EVERY kind (the filed pack-only scope was
a same-name confound: same-name re-exports already resolved through the
name-keyed fn_ast_map). scanDecls now follows ident-/ns.X-RHS const
alias chains (aliasedFnDecl; 0120's hop walk extracted as
followAliasChain) and registers the alias name in fn_ast_map
(absent-only), so every dispatch path — early pack/comptime/generic,
plain lazy-lower, plan-side typing — sees the target decl unchanged.
my_print :: s.print; / my_format :: s.format; now work (the std.sx
re-export shape). Regression: examples/0546 (+rich). Gates: zig build
test 0, suite 588/588.

readme.md

@@ -486,9 +486,10 @@ carry does not chain through a second flat hop.
 **Re-exporting through alias declarations.** Since visibility never chains,
 a facade re-exports another module's members as its OWN declarations —
 ordinary aliases, which its direct flat importers then see bare. This works
-for functions, plain types, and generic struct heads alike (the generic
-alias binds the same template, so instantiation and methods resolve
-through it):
+for functions of every kind (plain, generic, comptime-pack like `print`),
+plain types, and generic struct heads alike (the generic alias binds the
+same template, so instantiation and methods resolve through it), renamed
+or same-name:
 
 ```sx
 // facade.sx