Fix #210: declare missing delete-button column in saved pastes table

/mine rows render 7 cells (ID + delete button) but the colgroup and
thead only declared 6 columns, so under table-layout:fixed the delete
button cell overlapped the ID column at narrower widths. Add a
col-del column + empty header th to match the row cells.

internal/web/static/app.css

@@ -832,6 +832,9 @@ button[type="submit"]:focus-visible,
 .col-a { width: 260px; } .col-b { width: 140px; } .col-c { width: 120px; }
 .col-d { width: 96px; } .col-d2 { width: 150px; } .col-e { width: 190px; }
 .col-f { width: 100px; } .col-g { width: 190px; }
+/* #210: /mine rows render a delete button cell that had no declared column,
+   so under table-layout:fixed it overlapped the ID column. */
+.col-del { width: 64px; }
 .spacer-flex { flex: 1; }
 .input-num { width: 80px; }
 .input-num-sm { width: 64px; }