i18n(migrate,sweep): translate status/error strings + add a hygiene regression guard

- The import-key sweep and migrate-to-seed flows set several user-visible
  status/error strings (shown via sweep_status_ / seed_migration_status_ /
  rescan_status) as bare English; routed them through TR() with additive keys.
- Extended scripts/check-source-hygiene.sh with two low-false-positive content
  guards so this debt can't regrow: a bare-English migrate/sweep status
  assignment, and a Tactile button sized with a raw (unscaled) pixel literal.
  Passes clean on the tree (362 files); the dev sweep harness is allowlisted.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

scripts/check-source-hygiene.sh

@@ -48,6 +48,36 @@ for f in "${files[@]}"; do
     fi
 done
 
+# ── Content guards (UX-hygiene threads) ──────────────────────────────────────
+# Low-false-positive regression checks for debt the UX audit cleared, so it can't
+# silently regrow. Each is deliberately narrow; widen only with an allowlist.
+for f in "${files[@]}"; do
+    [[ "$f" == *.cpp ]] || continue
+    [[ -f "$f" ]] || continue
+    # app_sweep.cpp is the dev screenshot-sweep harness: its fixture strings are never shipped UI.
+    [[ "$(basename "$f")" == "app_sweep.cpp" ]] && continue
+
+    # (1) Tactile button sized with a raw multi-digit pixel literal that ignores HiDPI.
+    #     Real sizes multiply by ui::Layout::dpiScale() / dp / hScale, or come from schema.
+    if hits=$(grep -nE 'Tactile(Small)?Button\([^;]*ImVec2\([1-9][0-9]+(\.[0-9]+f?)?,' "$f" \
+                | grep -vE 'dpiScale|\* *dp\b|\* *hdpi|hScale|schema|Scale\('); then
+        while IFS= read -r line; do
+            echo "✗ unscaled button size (multiply the px by ui::Layout::dpiScale()): $f:$line" >&2
+            fail=1
+        done <<< "$hits"
+    fi
+
+    # (2) User-visible migrate/sweep status assigned a bare English literal instead of TR(...).
+    #     "__SENTINEL__" comparisons and empty strings are fine.
+    if hits=$(grep -nE '(sweep_status_|seed_migration_status_)[[:space:]]*=[[:space:]]*"[A-Za-z]' "$f" \
+                | grep -vE 'TR\(|"__'); then
+        while IFS= read -r line; do
+            echo "✗ untranslated status string (route through TR(...)): $f:$line" >&2
+            fail=1
+        done <<< "$hits"
+    fi
+done
+
 if (( fail )); then
     echo "" >&2
     echo "Source hygiene check failed. See docs in scripts/check-source-hygiene.sh." >&2