feat(oxibadge): add settings screen for shifts, rounding and language

Add a settings screen (gear button on the month-confirmation screen)
to configure the expected shift times, the rounding step, the
interface language, and the time clock address — replacing the old
onboarding-only connection flow. Settings persist to the same
preferences.toml as the reader address, under a single load_settings/
save_settings command pair.

The review screen's "fix shifts" action now redistributes stacked
punches by nearest configured shift time instead of blind position,
and a stacked cell manually cleared down to one entry no longer
leaves a dangling empty input.

Assisted-by: Claude Sonnet 5 <noreply@anthropic.com>

oxibadge/src/lib/locales/en.json

@@ -115,5 +115,47 @@
     "back_to_review": "Back to review",
     "round_and_export": "Round and export",
     "export_anyway": "Export anyway"
+  },
+  "settings": {
+    "title": "Settings",
+    "device_title": "Time clock",
+    "device_desc": "The time clock Oxibadge downloads punches from.",
+    "device_label": "Address",
+    "status_testing": "Checking…",
+    "status_ok": "Reachable",
+    "status_idle": "Not verified",
+    "edit_address": "Edit address",
+    "test_connection": "Test connection",
+    "ip_label": "IP address",
+    "port_label": "Port",
+    "ip_invalid": "Invalid format, e.g. 192.168.1.100",
+    "cancel": "Cancel",
+    "confirm": "Confirm",
+    "shifts_title": "Expected shifts",
+    "shifts_desc": "The standard work schedule. The break between the two shifts is the one used by \"Add lunch break\" in the review.",
+    "shift_1": "1st shift",
+    "shift_2": "2nd shift",
+    "shift_in": "In",
+    "shift_out": "Out",
+    "shift_error_format": "Enter all times in HH:MM format.",
+    "shift_error_out1": "The 1st shift's clock-out must be after its clock-in.",
+    "shift_error_in2": "The 2nd shift must start after the 1st one ends.",
+    "shift_error_out2": "The 2nd shift's clock-out must be after its clock-in.",
+    "hours_per_day_label": "Expected hours",
+    "per_day": "per day",
+    "break_label": "Break",
+    "round_title": "Time rounding",
+    "round_desc": "Times are rounded to the nearest multiple.",
+    "round_example": "E.g. {from} → {to}.",
+    "round_label": "Minutes",
+    "minutes_short": "min",
+    "round_range": "From 1 to 60 minutes",
+    "language_title": "Language",
+    "language_desc": "Oxibadge's interface language.",
+    "save_idle": "Changes are saved automatically",
+    "save_saving": "Saving…",
+    "save_saved": "Changes saved",
+    "save_invalid": "Not saved: fix the error",
+    "save_failed": "Save failed"
   }
 }