fix(makedata): shorten the DC_MAXCELLS_WEBEDIT description to fit var_desc

MPE_CONFIG.VAR_DESC is varchar(300), but the description written for
DC_MAXCELLS_WEBEDIT is 336 characters, so the insert truncates it.  The
truncation raises a WARNING, which sets SYSCC, and makedata aborts on
`&syscc ne 0` immediately after %mpe_makedata():

    WARNING: Character expression will be truncated when assigned to
      character column var_desc.
    ERROR: Execution terminated by an ABORT CANCEL statement

The abort happens before the settings job is written, so a fresh deploy
ends with no control library and no settings.sas at all.  It goes
unnoticed because the SAS test suite reuses whatever library is already
on the estate - the first time it bites is a deploy from scratch.

The description is shortened to 201 characters in both places it is
written - mpe_makedata (new installs) and the 20261003 row/cell limits
migration (existing installs).  The rationale it carried is user-visible
help text, so it moves to a SAS comment above each insert rather than
being dropped.

Verified on a real Viya estate, deploying from scratch:
  - before: makedata aborted, "Err during VIYA1337 build", no settings.sas
  - after:  makedata completed with zero warnings, and the SAS test suite
            then ran 59/59 green

sas/sasjs/db/migrations/20261003_row_and_cell_limits.sas

@@ -97,6 +97,10 @@ quit;
       set tx_to=&now
       where var_name='DC_MAXCELLS_WEBEDIT' and var_active=1 and &now lt tx_to;
 
+    /* Why the cell limit exists, kept out of var_desc - MPE_CONFIG.VAR_DESC
+      is varchar(300), and a truncation WARNING aborts the build.  A wide
+      table is expensive long before it is tall - 250 rows of a 1000 column
+      table is a quarter of a million cells. */
     insert into &dclib..mpe_config
       set tx_from=&now
         ,tx_to='31DEC9999:23:59:59'dt
@@ -106,10 +110,8 @@ quit;
         ,var_active=1
         ,var_desc='This sets the maximum number of CELLS (rows multiplied by'
           !!' columns) that can be loaded into the browser for editing in the'
-          !!' EDIT screen.  It exists because a wide table is expensive long'
-          !!' before it is tall - 250 rows of a 1000 column table is a quarter'
-          !!' of a million cells.  Whichever of this and DC_MAXOBS_WEBEDIT is'
-          !!' reached first applies.';
+          !!' EDIT screen.  Whichever of this and DC_MAXOBS_WEBEDIT is reached'
+          !!' first applies.';
   quit;
 %end;
 %else %do;

sas/sasjs/macros/mpe_makedata.sas

@@ -79,6 +79,10 @@ insert into &lib..mpe_config set
       !!' will require a decent browser (ie, not IE) and more memory on the'
       !!' client side.  The DC_MAXCELLS_WEBEDIT limit is applied at the same'
       !!' time, whichever is reached first.';
+/* Why the cell limit exists, kept out of var_desc - MPE_CONFIG.VAR_DESC is
+  varchar(300), and a truncation WARNING aborts this whole build.  A wide
+  table is expensive long before it is tall - 250 rows of a 1000 column
+  table is a quarter of a million cells. */
 insert into &lib..mpe_config set
     tx_from=0
     ,tx_to='31DEC9999:23:59:59'dt
@@ -88,9 +92,7 @@ insert into &lib..mpe_config set
     ,var_active=1
     ,var_desc='This sets the maximum number of CELLS (rows multiplied by'
       !!' columns) that can be loaded into the browser for editing in the EDIT'
-      !!' screen.  It exists because a wide table is expensive long before it'
-      !!' is tall - 250 rows of a 1000 column table is a quarter of a million'
-      !!' cells.  Whichever of this and DC_MAXOBS_WEBEDIT is reached first'
+      !!' screen.  Whichever of this and DC_MAXOBS_WEBEDIT is reached first'
       !!' applies.';
 insert into &lib..mpe_config set
     tx_from=0