refactor(ui): mint the text-2xs token and the neutral TagChip

Three integration cards carried the same hand-copied chip literal in the
card-header accessory slot, each free to drift on the next touch; the size
itself was an arbitrary value repeated at three slightly different spellings
across the tree.

- Mint `--text-2xs` (0.6875rem with a matched line-height) as the one
  sanctioned step below `text-xs`.
- Mint `TagChip` and adopt it on the Fitbit, Google Health, and Nightscout
  cards. It stays distinct from `Badge`, which carries status meaning.
- Sweep the arbitrary micro sizes: the stepper label and the two dose-ledger
  outline badges move onto the token; the muted target caption and the muted
  ledger meta row move up to the `text-xs` muted floor.

No visible change beyond the two muted rows gaining a fraction of a pixel.

src/components/medications/dose-history-ledger.tsx

@@ -623,7 +623,7 @@ function LedgerRowItem({
             {t(`medications.detail.verlauf.status.${row.status}`)}
           </span>
           {row.kind === "ad_hoc" && (
-            <Badge variant="outline" className="text-[0.65rem]">
+            <Badge variant="outline" className="text-2xs">
               {t("medications.detail.verlauf.adHocTag")}
             </Badge>
           )}
@@ -634,7 +634,7 @@ function LedgerRowItem({
           {row.kind === "slot" && row.pinned && (
             <Badge
               variant="outline"
-              className="text-[0.65rem]"
+              className="text-2xs"
               data-slot="ledger-pinned-badge"
             >
               {t("medications.detail.verlauf.pin.pinnedTag")}
@@ -862,7 +862,7 @@ function LedgerSummaryChart({
           style={{ width: `${pct(missed)}%` }}
         />
       </div>
-      <div className="text-muted-foreground flex flex-wrap gap-x-3 gap-y-0.5 text-[0.7rem]">
+      <div className="text-muted-foreground flex flex-wrap gap-x-3 gap-y-0.5 text-xs">
         <span className="text-success">
           {t("medications.detail.verlauf.status.taken_on_time")}: {takenOnTime}
         </span>

src/components/medications/wizard/wizard-stepper.tsx

@@ -162,7 +162,7 @@ export function WizardStepper({
                   />
                   <span
                     className={cn(
-                      "max-w-[6rem] truncate text-[0.6875rem] leading-none",
+                      "text-2xs max-w-[6rem] truncate leading-none",
                       isActive
                         ? "text-foreground font-medium"
                         : "text-muted-foreground",