Tree cards: render unset-sex / redacted "Living person" in gray, not blue

The chart mapped gender as `=== "female" ? "F" : "M"`, so anything non-female —
including null — became "M" (blue). On the public site, redacted living people
(whose gender the privacy engine nulls) all showed blue regardless of real sex,
and anywhere a person's sex was simply unset they also showed blue (misleading).

Map male→"M", female→"F", and everything else→null, which family-chart renders
as `card-genderless`. So living/redacted people render gray (and never imply a
sex), and unset-sex people render gray instead of defaulting to male/blue.
Applied to both the member tree (tree/page.tsx) and the public chart
(public-tree-chart.tsx), which share chart.css. Also bumped the genderless color
from the library's washed-out `lightgray` to a warm mid-gray that matches the
muted male/female tones and the brand palette.

Privacy note: `_redact` already nulls gender, so this is purely the client color
mapping — no sex leak, just a correct neutral rendering.

Signed-off-by: Justin Paul <justin@jpaul.me>

frontend/app/trees/[id]/tree/chart.css

@@ -1,7 +1,10 @@
 .f3 {
   --female-color: rgb(196, 138, 146);
   --male-color: rgb(120, 159, 172);
-  --genderless-color: lightgray;
+  /* Warm mid-gray for unset-sex / redacted "Living person" cards — matches the
+     muted male/female tone weight and the brand palette, instead of the library's
+     washed-out lightgray. */
+  --genderless-color: rgb(156, 150, 143);
   --background-color: rgb(33, 33, 33);
   --text-color: #fff;