Move cardToMiddle vertical-centering fix into the family-chart patch

Fold the fly-to vertical-centering fix into our patch-package patch (alongside
the existing spouse-layout fix) instead of compensating in app code, and revert
the in-app workaround so the two don't double-correct.

- patches/family-chart+0.9.0.patch: cardToMiddle now scales datum.y by the zoom
  k in both dist builds (.js + .esm.js), matching datum.x. Verified the patch
  applies cleanly (patch-package --error-on-fail).
- tree/page.tsx: the cardToMiddle caller passes raw y again (the patched library
  does the scaling now); pre-scaling here too would double-correct. Behavior is
  identical to the previous in-app fix — both center the node exactly.
- CLAUDE.md: documents the two family-chart patches, how to regenerate them, and
  that both should be upstreamed. The cardToMiddle fix is submitted upstream
  (donatso/family-chart#103, issue #102); the spouse-layout fix is a TODO.

The frontend Dockerfile already COPYs patches/ before npm ci, so the fix is in
the production build.

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

frontend/app/trees/[id]/tree/page.tsx

@@ -315,12 +315,12 @@ export default function TreePage() {
         try {
           const rect = svg.getBoundingClientRect();
           const scale = handlers.getCurrentZoom ? handlers.getCurrentZoom(svg).k : 1;
-          // family-chart's cardToMiddle scales datum.x by the zoom but NOT
-          // datum.y (a library bug), so vertical centering is only correct at
-          // scale 1 and drifts by datum.y·(k−1) otherwise — landing "below the
-          // tree". Pre-multiply y by the scale to cancel the missing ·k.
+          // cardToMiddle centers the datum at the current zoom. (Its vertical
+          // centering at non-1 zoom is fixed in our family-chart patch — see
+          // CLAUDE.md / upstream PR donatso/family-chart#103 — so we pass the
+          // raw y; do NOT pre-scale it here or it double-corrects.)
           handlers.cardToMiddle({
-            datum: { x: xy.x, y: xy.y * scale },
+            datum: xy,
             svg,
             svg_dim: { width: rect.width, height: rect.height },
             scale,