Source badge at the start of every log line

Each row now starts with a fixed-width badge naming its source, one color
per source: SYSLOG, DOCKER, KERNEL (dmesg), HOST (/var/log), AUDIT, FILE
and LS. The AUDIT/FILE/LS badges move there from before the app name; those
sources keep their colored edge and tint.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

web/index.html

@@ -140,6 +140,7 @@
 
   <div id="table" class="table" hidden>
     <div id="listHead" class="list-head" role="presentation">
+      <span data-col="src"><span class="lbl" data-i18n="colSrc">Source</span></span>
       <span data-col="rcv"><span class="lbl" data-i18n="colRcv">Received</span><i class="grip" data-i18n-title="colGrip"></i></span>
       <span data-col="mt"><span class="lbl" data-i18n="colMt">Message time</span><i class="grip" data-i18n-title="colGrip"></i></span>
       <span data-col="sev"><span class="lbl" data-i18n="colSev">Severity</span><i class="grip" data-i18n-title="colGrip"></i></span>