fix(brand): make the stamp's tagline survive rasterisation

SELF-HOSTED SMTP RELAY was set at font-size 7.2 with letter-spacing 2.8 —
a cap height of 5.2 in a 330-unit artwork, which puts its stems at about
half a device pixel where the mark is actually used. More than half the
line's ink came out as antialiasing: measured against the brown, the
typical tagline pixel reached 2.1:1 where the two colours are worth
7.3:1, and at 330px not one pixel reached full strength. The wordmark
above it renders 66% of its pixels solid.

It is now 11.5/0.15. The line keeps its footprint (154 units against
153) and its monospaced cells, fitted from the grid the outlines were
generated on; the width the tracking was spending went to the glyphs
instead, taking cap height to 8.3. Mean ink coverage goes 0.39 to 0.60
at the README's width and 0.33 to 0.47 at the 330px the login and setup
pages use.

opacity=".78" is gone with it. It cost 30% of the available contrast to
mark the line as secondary, which a 3.4:1 difference in size already
does, and it was multiplying the alpha of stems that were mostly alpha
to begin with.

A stroke to thicken the stems was measured and rejected: at 0.12-0.30 it
lifted mean coverage 0.59 to 0.63 while dropping the share of solid
pixels, since it adds antialiased edges rather than filling stems.

internal/web/static/logo.svg is a byte copy of the docs asset and stays
one. selfpost-proof.html carries the lockup as live text and is where
the metrics come from, so it moves too, or the next regeneration would
put the old spec back.

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

CHANGELOG.md

@@ -52,6 +52,17 @@ Format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/); version
 
 ### Changed
 
+- The stamp's `SELF-HOSTED SMTP RELAY` line is set at 11.5/0.15 instead of
+  7.2/2.8, and no longer carries `opacity=".78"`. At the old size its stems
+  rasterised to about half a device pixel, so more than half its ink landed
+  as antialiasing — the typical pixel reached 2.1:1 against the brown rather
+  than the 7.3:1 the two colours are worth, and none reached full strength.
+  The line keeps its footprint and its monospaced cells: the width the
+  tracking was spending went to the glyphs, whose cap height rises from 5.2
+  to 8.3. The mark is used at 330px on the login and setup pages, which is
+  where this was worst. `internal/web/static/logo.svg` is a copy of
+  `docs/assets/selfpost-stamp.svg` and both carry the change, as does the
+  proof sheet the outlines are drawn from.
 - The delivery log lists what identifies a message and nothing else: time,
   sender, recipient, subject, status. Domain and application, which were a
   column each, remain the log's two filters and now appear per message on the