docs: compare three panel headers against the current one

At nav size the stamp cannot carry itself: its perforation is under a
pixel and its brick field dissolves into the brick bar, leaving a thin
frame around the name. The perforated edge under the bar was also drawn
inverted - round bumps with pointed gaps, where a real perforation is
round holes with flat teeth.

header/ puts the current header beside three replacements on a real
page: A, the wordmark alone with round holes of page colour bitten into
the bar at the mark's own hole-to-tooth ratio; B, the wordmark on a plain
bar; C, a stamp-paper header with an ink hairline, the mark's
perforation, and brick only behind the name. The wordmark files are the
stamp's own outlines, cut out of selfpost-stamp-compact.svg.

A comparison sheet pending the owner's choice; the 33 mockups and the
design contract are unchanged. Also tracks .claude/launch.json, the
local static server the mockups are previewed with.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/assets/panel-redesign/header/perf-edge.svg

@@ -0,0 +1,4 @@
+<svg xmlns="http://www.w3.org/2000/svg" width="16" height="7" viewBox="0 0 16 7">
+<path d="M0 0H16V6H13A5 5 0 0 0 3 6H0Z" fill="#F3EDE1"/>
+<path d="M0 6H3A5 5 0 0 1 13 6H16" fill="none" stroke="#12161C" stroke-width="0.7"/>
+</svg>