fix(shell): return to the list's scroll position on Back

Back from a detail page (a biomarker, a medication, a workout) opened
the list at the top. The shell scrolls inside `<main>`, which stays
mounted across routes, and the browser's own restoration only moves
the document. Nothing kept the list's offset, so `<main>` stayed where
the detail page had left it; and the one-shot skip on `popstate` was
cleared by a timer that could run before the restored page rendered,
in which case the forward-navigation reset fired anyway.

The shell now records `<main>`'s offset per address while scrolling,
reads it back on `popstate` and applies it once the page has rendered,
retrying for up to a second while a list is still shorter than the
offset. A forward navigation still starts at the top.

src/__tests__/baselines/source-function-lines.json

@@ -138,7 +138,7 @@
     "components/labs/lab-history-list.tsx :: LabHistoryList": 534,
     "components/labs/ocr-review-dialog.tsx :: OcrReviewDialog": 359,
     "components/labs/ocr-row-editor.tsx :: OcrRowEditor": 378,
-    "components/layout/auth-shell.tsx :: AuthShell": 518,
+    "components/layout/auth-shell.tsx :: AuthShell": 484,
     "components/layout/bottom-nav.tsx :: BottomNav": 262,
     "components/layout/capture-picker.tsx :: CapturePicker": 235,
     "components/layout/sidebar-nav.tsx :: SidebarNav": 356,

src/__tests__/baselines/version-stamp-comments.json

@@ -1,7 +1,7 @@
 {
   "$comment": "Comment lines that open with a release version, per file under src/. Maintained by src/__tests__/version-stamp-ratchet.test.ts.",
   "count": 2892,
-  "total": 9216,
+  "total": 9215,
   "entries": {
     "__tests__/account-payload-consumer-guard.test.ts": 2,
     "__tests__/acting-account-boundary-guard.test.ts": 7,
@@ -1096,7 +1096,7 @@
     "components/layout/__tests__/shared-record-chrome.test.tsx": 1,
     "components/layout/__tests__/sidebar-nav.test.tsx": 3,
     "components/layout/account-switcher-menu.tsx": 1,
-    "components/layout/auth-shell.tsx": 14,
+    "components/layout/auth-shell.tsx": 13,
     "components/layout/bottom-nav.tsx": 8,
     "components/layout/capture-picker.tsx": 5,
     "components/layout/nav-model.ts": 17,