refactor(ui): give Settings and Admin one card rhythm and one page header

The two consoles used the same primitives and still read as two systems,
because everything without a primitive had drifted: the header-to-body
step existed in three competing techniques at once (`mt-4` on the first
body child, `space-y-4` on the card, `mb-4` on the header), the body
started either at the card edge or 28 px in, and both shells hand-rolled
the page title instead of calling `PageHeader`.

Move the decisions into the primitives so a call site cannot re-open them:

- `SettingsCard` is gap-based like `Card` (`flex flex-col gap-4`). The
  header-to-body step is the container's, not a margin somebody remembers.
  A dense card still overrides the gap on the card itself.
- The body starts at the card edge. `pl-7` is gone — off the spacing scale,
  and it mis-aligned action rows against their own forms wherever two
  neighbouring cards disagreed about it.
- The card header's description slot loses its `space-y-1`. That was the
  licence call sites used to stack explainer paragraphs into a muted
  `text-xs` slot; the slot holds one sentence.
- New `SettingsCardActions`: one action row, trailing edge, last thing in
  the card. `align="start"` spells the one exception, a card whose only
  actions are links out.
- New `StatTile` replaces four hand-rolled label/value boxes in Admin.
- `SectionHeading` moves from `insights/` to `ui/`. It is the heading above
  a group of cards, which is what Settings needs; Settings had been using a
  card header with no card, which reads as a card that failed to paint.

Both shells now render their heading through `PageHeader`, which gained
`headingAs="div"` for the second copy each shell paints (mobile above the
nav strip, desktop inside the grid) so only one is a real `<h1>`. The
page explainer is muted everywhere: the primitive said foreground, the
standards and every hand-rolled copy said muted, so pages disagreed with
each other. Medications, Vorsorge, the labs / custom-metric / illness
detail pages and the clinician view drop their hand-rolled title blocks
too, including the mid-word truncation on the medications subtitle.

Tests pin the parts that can be checked exactly: the card's gap, the
description slot's missing rhythm, the action row's two alignments, the
`<h1>`-free shells, and a sweep asserting `pl-7` stays gone.

src/components/settings/access/grant-invite-card.tsx

@@ -148,7 +148,7 @@ export function GrantInviteCard() {
         title={t("recordSharing.invite.title")}
         description={t("recordSharing.invite.description")}
       />
-      <form onSubmit={submit} className="mt-4 space-y-3">
+      <form onSubmit={submit} className="space-y-3">
         <div className="space-y-1.5">
           <Label htmlFor="grant-invite-identifier">
             {t("recordSharing.invite.identifierLabel")}

src/components/settings/access/grants-given-card.tsx

@@ -52,7 +52,7 @@ export function GrantsGivenCard() {
         title={t("recordSharing.given.title")}
         description={t("recordSharing.given.description")}
       />
-      <div className="mt-4">
+      <div>
         {isLoading && (
           <Loader2
             className="text-muted-foreground size-5 animate-spin motion-reduce:animate-none"

src/components/settings/access/grants-received-card.tsx

@@ -68,7 +68,7 @@ export function GrantsReceivedCard() {
         title={t("recordSharing.received.title")}
         description={t("recordSharing.received.description")}
       />
-      <div className="mt-4">
+      <div>
         {isLoading && (
           <Loader2
             className="text-muted-foreground size-5 animate-spin motion-reduce:animate-none"

src/components/settings/access/managed-profile-card.tsx

@@ -75,7 +75,7 @@ export function ManagedProfileCard() {
         title={t("recordSharing.managed.title")}
         description={t("recordSharing.managed.description")}
       />
-      <div className="mt-4 space-y-4">
+      <div className="space-y-4">
         {/* Content, not meta: this is what somebody is consenting to take on,
             and UI-STANDARDS §3 reserves muted for the incidental. */}
         <p data-slot="managed-profile-explainer" className="text-sm">

src/components/settings/access/record-activity-card.tsx

@@ -50,7 +50,7 @@ export function RecordActivityCard() {
         title={t("recordSharing.activity.title")}
         description={t("recordSharing.activity.description")}
       />
-      <div className="mt-4 space-y-3">
+      <div className="space-y-3">
         {/* The window, stated. Rendered only once the server has said what it
             is — a placeholder number here would be exactly the invented value
             the sentence exists to avoid. */}