style(web): align --link with the accent blue (#4183c4)

`--link` was still the brighter GitHub blue while everything else moved to
Gitea's #4183c4, so links read as a second, slightly different accent. One blue
now.

Contrast on this palette: 4.50:1 on --panel (#161718), 4.14:1 on --bg
(#1e1f20), 3.77:1 on --panel-2 (#22272e) — down from 4.79 / 4.41 / 4.01. Body
links sit on --panel and stay above the 4.5:1 AA threshold; the ones on the
darker surfaces (nav hover, table cells) land between AA-large and AA, as the
rest of this palette's dim text already does.

src/ci_orchestrator/web/static/app.css

@@ -21,7 +21,7 @@
   --success: #3fb950;
   --danger: #f85149;
   --warn: #d29922;
-  --link: #2f81f7;
+  --link: #4183c4;
   /* Single rounding token, matched to Gitea's `--border-radius` (~4px) so
    * cards, buttons, inputs, code, notices and badges all round identically.
    * The only intentional exception is the gauge/progress track (a pill). */