comptime VM: dedicated Type builtin TypeId (8B), distinct from .any — foundation (dead)

Add TypeId.type_value (slot 19) + matching TypeInfo.type_value variant: an
8-byte type handle, distinct from the 16-byte boxed .any. All types.zig layout
handlers wired (size/align 8, display "Type", hash/eql); toLLVMTypeInfo -> i64.

Reserve builtin headroom: first_user 19 -> 100 (slots 20-99 padded with the
unresolved tripwire) so future builtins don't renumber user TypeIds / churn
sx ir snapshots. 22 IR snapshots regenerated (pure renumber to 100-base).

type_resolver still returns .any for "Type" — nothing produces .type_value
yet, so no behavior change. 697/0 both gates.

src/backend/llvm/types.zig

@@ -97,6 +97,10 @@ pub const TypeLowering = struct {
                 return c.LLVMVectorType(elem, vec.length);
             },
             .any => self.e.getAnyStructType(),
+            // A comptime `Type` value is an 8-byte type handle (a `TypeId` in a
+            // word), distinct from the 16-byte boxed Any. It is comptime-only, but
+            // the type still lowers (dead comptime-body code / a global slot) as i64.
+            .type_value => self.e.cached_i64,
             .noreturn => self.e.cached_void,
             .@"struct" => |s| {
                 // Build LLVM struct type from fields