panel: restyle on the mark's own palette and type

The stamp was approved on its own sheet and the panel kept the blue-on-cool-grey
it shipped with, so the mark read as pasted onto someone else's page. Brick
becomes the accent, the greys warm to paper, and the corners square up towards
the stamp's own edge.

Brick is two tokens rather than one. #7A3B2E under white text is 8.4:1, but as
text on the dark scheme's background it is about 2:1 — a link nobody can read.
So --accent-fill carries controls and --accent-text carries links and the active
navigation entry; in the light scheme they coincide, in the dark one they do not.

IBM Plex ships with the panel instead of being named and hoped for. The mark is
Plex converted to outlines, so a system stack left the panel's own name as the
only Plex on the page — and ui-monospace resolves to Consolas, SF Mono or DejaVu
Sans Mono depending on the machine, which laid the send log and mail.log tables
out differently for every operator. Three WOFF2 files, 76 KB, served from the
panel's own origin so default-src 'self' still covers them.

Two things changed shape rather than colour. Links had no rule at all and ran on
the browser's blue, invisible while the accent was blue and wrong the moment it
was not. And the column-narrowing that login and setup had by name now keys off
the narrow card itself, so Settings and the user form stop splitting their
heading from the card it belongs to.

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

NOTICE

@@ -11,21 +11,28 @@ Corresponding Source for the published releases is at:
 If you modify SelfPost and let users interact with it over a network,
 AGPL-3.0 §13 requires you to offer them the Corresponding Source of
 your modified version. Update the Source link in the panel footer
-(internal/web/templates/layout.html) so it points at your sources.
+(internal/web/view/templates/layout.html) so it points at your sources.
 
 Third-party software included in this distribution
 ----------------------------------------------------
 
-htmx 2.0.4 (internal/web/static/htmx.min.js)
+htmx 2.0.4 (internal/web/view/static/htmx.min.js)
   Copyright (c) Big Sky Software
   Licence: Zero-Clause BSD (0BSD)
   https://github.com/bigskysoftware/htmx
 
-IBM Plex Sans / IBM Plex Mono (wordmarks in SVG logos only)
+IBM Plex Sans / IBM Plex Mono
   Copyright © 2017 IBM Corp., with Reserved Font Name "Plex"
   Licence: SIL Open Font License 1.1
-  The shipped SVGs use outlined paths derived from these fonts; the
-  font files themselves are not distributed.
+  https://github.com/IBM/plex
+  Distributed unmodified as three latin-subset WOFF2 files served by the
+  control panel:
+    internal/web/view/static/ibm-plex-sans.woff2      (variable, 100-700)
+    internal/web/view/static/ibm-plex-mono-400.woff2
+    internal/web/view/static/ibm-plex-mono-600.woff2
+  Subsetting and WOFF2 packaging by Fontsource (fontsource.org), from
+  the Google Fonts distribution. The wordmarks in the shipped SVG logos
+  are outlined paths derived from the same fonts.
 
 Go module dependencies are listed with their licences in
 docs/development.md § External libraries. Debian packages in the