Field groups: tighter style + apply to report

Form: dropped the boxed card treatment for FieldGroupCard in favor
of a leaf-tinted left rule + small uppercase mini-label. Eats only
~14px of horizontal space (border + pl-3/sm:pl-4) instead of
~32-40px for the previous bg-tinted card with px-4/sm:px-5 on both
sides, so the inner 2-col grid keeps more breathing room for the
fields themselves.

Report: same field-group concept now applies to ReportSection.
Grouped FieldHistoryRows render together inside a leaf-tinted left
rule with a small label above. Walk preserves the declared field
order — a group is emitted at its first member's position; the
other members are skipped when the loop later reaches them. Mixes
cleanly with the existing MembershipChart inline insertion and the
divide-y rhythm of standalone rows.

components/StageSection.tsx

@@ -348,9 +348,10 @@ function LockedBanner() {
 
 /**
  * Visual cluster of related fields inside a section (e.g. "Market Study"
- * grouping its date + upload fields). Renders as a quiet bordered card
- * with an optional heading; the fields inside use the same two-column
- * grid rules as the standalone per-field grid above/below.
+ * grouping its date + upload fields). Lightweight treatment: a leaf-tinted
+ * left rule and an optional uppercase mini-label. No boxed background or
+ * heavy padding — preserves the horizontal space the inner 2-col grid has
+ * to work with, while still signaling "these belong together."
  */
 function FieldGroupCard({
   label,
@@ -372,21 +373,26 @@ function FieldGroupCard({
   errors: FieldErrors;
 }) {
   return (
-    <div className="rounded-md border border-rule-soft bg-paper-2/30 px-4 py-4 sm:px-5 sm:py-5">
+    <div className="border-l-2 border-leaf-300/60 pl-3 sm:pl-4">
       {label && (
-        <h3 className="font-display text-sm font-medium uppercase tracking-[0.08em] text-ink-soft">
+        <h3 className="font-display text-[11px] font-medium uppercase tracking-[0.1em] text-ink-soft">
           {label}
         </h3>
       )}
       {intro && (
-        <p className={"max-w-prose text-xs leading-relaxed text-ink-mute " + (label ? "mt-1" : "")}>
+        <p
+          className={
+            "max-w-prose text-xs leading-relaxed text-ink-mute " +
+            (label ? "mt-0.5" : "")
+          }
+        >
           {intro}
         </p>
       )}
       <div
         className={
           "grid grid-cols-1 gap-x-7 gap-y-5 md:grid-cols-2 " +
-          (label || intro ? "mt-3" : "")
+          (label || intro ? "mt-2" : "")
         }
       >
         {fields.map((f) => {