chore(ui): unify heading weight, card cadence, and label-input gap across settings and admin

Sub-headings in the settings + admin section trees were mixing
font-medium and font-semibold; the password-change dialog used a
1.5-unit label-input gap while every other Settings form runs at 2.
Standardise on font-semibold for every h2 and h3, the card-internal
cadence to space-y-4 on the AI provider and thresholds-editor cards,
and lift the password-dialog field gaps to space-y-2.

src/components/admin/user-management-section.tsx

@@ -417,7 +417,7 @@ export function UserManagementSection() {
       {/* Edit Dialog */}
       {editingUser && (
         <div className="bg-muted/80 mt-4 rounded-lg p-4">
-          <h3 className="mb-3 text-sm font-medium">
+          <h3 className="mb-3 text-sm font-semibold">
             {t("admin.editUserTitle", { name: editingUser.username })}
           </h3>
           <div className="space-y-3">
@@ -484,7 +484,7 @@ export function UserManagementSection() {
       {/* Password Reset Dialog */}
       {resetUser && (
         <div className="bg-muted/80 mt-4 rounded-lg p-4">
-          <h3 className="mb-3 text-sm font-medium">
+          <h3 className="mb-3 text-sm font-semibold">
             {t("admin.resetPasswordTitle", { name: resetUser.username })}
           </h3>
           <div className="space-y-3">

src/components/settings/account-section.tsx

@@ -609,7 +609,7 @@ export function AccountSection() {
 
           <form onSubmit={handleChangePassword} className="space-y-3">
             <div className="grid gap-3 sm:grid-cols-3">
-              <div className="space-y-1.5">
+              <div className="space-y-2">
                 <Label htmlFor="current-password">
                   {t("settings.currentPassword")}
                 </Label>
@@ -619,7 +619,7 @@ export function AccountSection() {
                   onChange={(e) => setCurrentPassword(e.target.value)}
                 />
               </div>
-              <div className="space-y-1.5">
+              <div className="space-y-2">
                 <Label htmlFor="new-password">
                   {t("settings.newPassword")}
                 </Label>
@@ -629,7 +629,7 @@ export function AccountSection() {
                   onChange={(e) => setNewPassword(e.target.value)}
                 />
               </div>
-              <div className="space-y-1.5">
+              <div className="space-y-2">
                 <Label htmlFor="confirm-password">
                   {t("settings.confirmNewPassword")}
                 </Label>
@@ -707,7 +707,7 @@ function PasskeyListSection({ isAuthenticated }: { isAuthenticated: boolean }) {
   if (!passkeys || passkeys.length === 0) {
     return (
       <div>
-        <h3 className="text-sm font-medium">{t("settings.passkeys")}</h3>
+        <h3 className="text-sm font-semibold">{t("settings.passkeys")}</h3>
         <p className="text-muted-foreground mt-1 text-xs">
           {t("settings.noPasskeys")}
         </p>
@@ -717,7 +717,7 @@ function PasskeyListSection({ isAuthenticated }: { isAuthenticated: boolean }) {
 
   return (
     <div>
-      <h3 className="text-sm font-medium">
+      <h3 className="text-sm font-semibold">
         {t("settings.registeredPasskeys")}
       </h3>
       <p className="text-muted-foreground mt-1 text-xs">

src/components/settings/ai-section.tsx

@@ -249,7 +249,7 @@ function AiInsightsCard({ isAuthenticated }: { isAuthenticated: boolean }) {
   }
 
   return (
-    <div className="bg-card border-border space-y-6 rounded-xl border p-6">
+    <div className="bg-card border-border space-y-4 rounded-xl border p-6">
       <div className="flex flex-wrap items-start justify-between gap-2">
         <div className="flex items-center gap-2">
           <Sparkles className="text-primary h-5 w-5" />

src/components/settings/integrations-section.tsx

@@ -385,7 +385,7 @@ function WithingsCard({
           </a>
         )}
         <div className="space-y-3">
-          <h3 className="text-sm font-medium">
+          <h3 className="text-sm font-semibold">
             {t("settings.withingsCredentials")}
           </h3>
           <form onSubmit={handleSaveCredentials} className="space-y-3">

src/components/settings/thresholds-editor-section.tsx

@@ -117,7 +117,7 @@ export function ThresholdsEditorSection({ id }: { id: string }) {
   return (
     <div
       id={id}
-      className="bg-card border-border scroll-mt-28 space-y-5 rounded-xl border p-6"
+      className="bg-card border-border scroll-mt-28 space-y-4 rounded-xl border p-6"
     >
       {/* v1.4.19 A8 / F-07: page header `settings.sections.thresholds.*`
           already provides the title + description for this route, so the