mail: draw the envelope as a wireframe

The solid body read as a heavy white slab next to the outline glyphs, and
cce-mail now flies it as a bar button where that weight dominates. Outline
the body instead and draw the flap in the same white stroke: with no
filled face, the dark inset crease the solid panels use (terminal,
calendar) has nothing to sit on.

Stroke 4, the outline weight of preview's frame and calendar's hangers.
Body corners stay squircle r=4.5 per folder.svg, the path inset by the
half-stroke so the stroked outer edge lands on the old silhouette.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

 svg/mail.svg | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/svg/mail.svg b/svg/mail.svg
index c3d16b1..db3b25a 100644
--- a/svg/mail.svg
+++ b/svg/mail.svg
@@ -1,7 +1,18 @@
 <svg width="40" height="40" viewBox="0 0 40 40" xmlns="http://www.w3.org/2000/svg">
-  <!-- Stylized envelope: rounded body + flap crease -->
-  <rect x="4" y="8" width="32" height="24" rx="4" fill="#ffffff" />
-  <!-- Flap crease -->
-  <path d="M7 12 L20 22 L33 12" fill="none" stroke="#282a36" stroke-width="3"
-        stroke-linecap="round" stroke-linejoin="round" opacity="0.35" />
+  <!-- Envelope, wireframe: an open body outline with the flap crease drawn
+       in the same white stroke rather than the dark inset treatment the
+       solid panels use (terminal.svg, calendar.svg) — there is no filled
+       face here for a crease to sit on. Stroke 4, the outline weight of
+       preview.svg's frame and calendar.svg's hangers. Body corners are
+       squircle (continuous-curvature) cubics, r=4.5, as in folder.svg: the
+       curve spans 1.5r from each corner with control points at 0.5r. The
+       body path is inset 2 (the half-stroke) from the solid glyph's old
+       4..36 x 8..32 silhouette, so the stroked outer edge lands where the
+       filled rect's edge used to. The flap's caps end inside the side
+       walls, where the two strokes merge. -->
+  <g fill="none" stroke="#ffffff" stroke-width="4" stroke-linecap="round"
+     stroke-linejoin="round">
+    <path d="M12.75 10 L27.25 10 C31.75 10, 34 12.25, 34 16.75 L34 23.25 C34 27.75, 31.75 30, 27.25 30 L12.75 30 C8.25 30, 6 27.75, 6 23.25 L6 16.75 C6 12.25, 8.25 10, 12.75 10 Z" />
+    <path d="M7.5 12.5 L20 22.5 L32.5 12.5" />
+  </g>
 </svg>