panel: give each nav entry an icon

The bar was six similar-length words; nothing distinguished them at a
glance. Each entry now leads with a 16px inline SVG.

Inline rather than an icon font or a sprite file: the icons inherit the
entry's colour through currentColor, so the active pill's darker text and
a link's blue need no second rule, they cost no request, and they need no
exemption from the panel's default-src 'self' policy. Each is aria-hidden
because the entry's text is already its accessible name.

Account is included -- it is a page like the others and would otherwise
be the one bare word left in the bar -- so the highlight and padding
rules now cover the session block too, and the bar centres its items
instead of aligning them on the text baseline now that an entry is an
icon-plus-label row rather than a run of text.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -25,6 +25,12 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
   `/mail-queue` (was `/queue`), System log at `/system-log` (was `/logtail`).
   Bookmarks to the old paths stop working.
 
+- panel: each entry in the navigation bar now carries an icon beside its label,
+  so the bar is scannable at a glance instead of a row of similar-length words.
+  The icons are inline SVG drawn in the entry's own colour — no extra request,
+  no exemption from the panel's Content-Security-Policy — and are hidden from
+  screen readers, which still announce the label alone.
+
 ## [0.2.0] - 2026-08-03
 
 - panel: every authenticated page now ends with the running version