Fix over-broad .log-table header fix: lh.php/localtx.php are mixed-align

The previous commit (4c58f85f) put class="log-table" on lh.php and
localtx.php too, which forced *every* header left - but only
Time/Mode/Callsign/Target are actually align="left" in those two
files. Source/Duration/Loss/BER have no align attribute at all (plain
<td>), so they were already correctly centered - the blanket fix just
moved the misalignment from the first 4 columns to the last 4.

Replace with a new `.al` class applied only to the specific <th>
elements whose column is genuinely align="left", leaving
Source/Duration/Loss/BER headers on the sitewide centered default to
match their centered data. last_herd.php/local_tx.php are untouched -
every column in those two really is align="left", so table.log-table
(all headers) remains correct there.

css/pistar-css-mini.php

@@ -614,11 +614,15 @@ table th {
     border-bottom: 2px solid var(--accent);
 }
 
-/* See css/pistar-css.php for why this is scoped to .log-table only. */
+/* See css/pistar-css.php for why there are two variants here. */
 table.log-table th {
     text-align: left;
 }
 
+th.al {
+    text-align: left;
+}
+
 table tr:nth-child(even) {
     background: var(--table-even);
 }