ffi M5.A.next.4A.bare.4.B: tryLowerReflectionCall splits static vs dynamic

Fix for the silent .s64 fall-through in `type_name(<dynamic-arg>)`.
`tryLowerReflectionCall` now splits on `isStaticTypeArg(node)`:
- Static (type_expr / identifier / pack_index_type_expr / pointer
  / array / slice / optional / many_pointer / function_type_expr
  / tuple_literal / call) → fold to const_string at lower time
  (today's fast path).
- Dynamic (index_expr, field_access, runtime locals, anything
  else) → emit `callBuiltin(.type_name, [arg_ref])`. The interp's
  arm (commit 9600ba5) reads the runtime `.type_tag` Value and
  returns the per-position name.

`isStaticTypeArg(node)` is a new helper mirroring the explicit
arms of `resolveTypeArg`. Lives alongside resolveTypeArg in
lower.zig; documented to track shape changes together.

emit_llvm: the comptime reflection builtins (`type_name`,
`type_eq`, `has_impl`) now emit a silent undef-i64 placeholder.
Same reasoning as 4A.bare.1.B's relaxation of const_type's
emit_llvm arm: the JIT compiles the containing fn module-wide
even if main never calls it, so emit-time noise here is just
dead-from-main's-perspective code. Real misuse — passing a non-
Type value to one of these — is caught by the interp arm's
`asTypeId orelse bailDetail`.

`examples/171-pack-dynamic-type-name.sx` flips from "s64s64"
(silent .s64 fold per element) to "s64string" (per-position
correct via interp arm). Test runs `walk(42, "hi")` at `#run`
time so the dynamic path executes in the interp.

211/211 example tests + zig build test green.

src/ir/emit_llvm.zig

@@ -2968,15 +2968,17 @@ pub const LLVMEmitter = struct {
                         self.advanceRefCounter();
                     },
                     .type_name, .type_eq, .has_impl => {
-                        // Comptime-only reflection builtins. Reaching
-                        // LLVM emit means lowering DIDN'T fold the call
-                        // (static-arg fast path) AND lowering emitted a
-                        // real `builtin_call` — but the resulting IR
-                        // shouldn't survive past the comptime interp
-                        // that's supposed to consume it. Loud failure:
-                        // log + undef placeholder so the LLVM verifier
-                        // catches downstream use.
-                        std.debug.print("emit_llvm: comptime reflection builtin '{s}' reached runtime emit — Type values are interp-only.\n", .{@tagName(bi.builtin)});
+                        // Comptime-only reflection builtins. When the
+                        // lowering split between static-fold and
+                        // dynamic-builtin-call routes a call to one of
+                        // these, the call site is intended for the
+                        // interp's arm. LLVM still compiles the
+                        // containing fn (the JIT module-wide) even if
+                        // main never calls it — so this op DOES reach
+                        // emit, just in dead-from-main's-perspective
+                        // code. Silent undef-i64 placeholder is the
+                        // right answer; the interp's arm catches real
+                        // misuse via `asTypeId orelse bailDetail`.
                         self.mapRef(c.LLVMGetUndef(self.toLLVMType(instruction.ty)));
                     },
                     else => {