feat(water-log): add 'holes' unit + EN/ES language toggle for mobile

- 'holes' / 'hoyos' added to MOBILE_UNITS alongside CFS/GPM/gal/ac-in/ac-ft
  with integer-only validation: submit button greys out and the keyboard
  raises the numeric keypad (no decimal) when the unit is selected.
- Language toggle in the headgate list header (next to logout) flips
  every screen between English and Spanish. Choice is persisted to the
  existing 'wl_lang' cookie for 1y, so the user's last selection
  sticks across logout/relogin.
- i18n strings lifted into shared src/lib/water-log/i18n.ts (single
  source of truth, en/es parity enforced by tests). All mobile screens
  (Pin, HeadgateList, LogForm, Success) plus the loadHeadgates error
  in the orchestrator consume the dictionary. Brand strip, aria-labels,
  segmented control labels, success recap, and submit-button labels
  all go through getT()/formatUnit()/displayUnit().
- 26 new unit tests (tests/unit/water-log-i18n.test.ts) cover: en/es
  dict parity, holes catalog + hoyos translation, all the
  detectInitialLang() branches (SSR/cookie/navigator), setLangCookie
  read/write, label interpolation helpers, and the unit catalog.

Refs /tmp/refactor-water-log.md (Commit B plan)

src/lib/water-log/i18n.ts

@@ -45,6 +45,14 @@ export type Labels = {
     save: string;
     saving: string;
     back: string;
+    signOut: string;
+    a11yBackToHeadgates: string;
+    a11yChangeHeadgate: string;
+    a11ySignOut: string;
+  };
+  /** The brand strip shown on the PIN and Success screens. */
+  brand: {
+    waterLog: string;
   };
   /** `/water` PIN entry screen. */
   pin: {
@@ -54,6 +62,8 @@ export type Labels = {
     unlock: string;
     forgot: string;
     genericError: string;
+    a11yPin: string;
+    a11yPinEntry: string;
   };
   /** `/water` headgate list screen. */
   headgates: {
@@ -65,14 +75,19 @@ export type Labels = {
     pullToRefresh: string;
     thresholdHigh: string;
     thresholdLow: string;
+    refresh: string;
+    refreshing: string;
+    loadError: string;
   };
   /** `/water` measurement entry screen. */
   log: {
     title: string;
     measurement: string;
+    unit: string;
     timestamp: string;
     loggedNow: string;
     notes: string;
+    notesOptional: string;
     notesPlaceholder: string;
     notesVisibility: string;
     measurementError: string;
@@ -124,6 +139,13 @@ export const LABELS: Record<Lang, Labels> = {
       save: "Save",
       saving: "Saving…",
       back: "Back",
+      signOut: "Sign out",
+      a11yBackToHeadgates: "Back to headgates",
+      a11yChangeHeadgate: "Change headgate",
+      a11ySignOut: "Sign out",
+    },
+    brand: {
+      waterLog: "TUXEDO WATER LOG",
     },
     pin: {
       title: "Enter your PIN",
@@ -132,6 +154,8 @@ export const LABELS: Record<Lang, Labels> = {
       unlock: "Unlock",
       forgot: "Forgot your PIN? Ask the ditch supervisor.",
       genericError: "Something went wrong. Try again.",
+      a11yPin: "PIN",
+      a11yPinEntry: "PIN entry — tap to focus",
     },
     headgates: {
       title: "Headgates",
@@ -143,13 +167,18 @@ export const LABELS: Record<Lang, Labels> = {
       pullToRefresh: "Pull down to refresh the list",
       thresholdHigh: "Hi",
       thresholdLow: "Lo",
+      refresh: "Refresh",
+      refreshing: "Checking…",
+      loadError: "Couldn't load headgates. Pull down to try again.",
     },
     log: {
       title: "Log Reading",
       measurement: "Measurement",
+      unit: "Unit",
       timestamp: "Timestamp",
       loggedNow: "Logged now",
       notes: "Notes",
+      notesOptional: "optional",
       notesPlaceholder:
         "Anything the supervisor should know about this reading?",
       notesVisibility: "Visible to admins only",
@@ -197,6 +226,13 @@ export const LABELS: Record<Lang, Labels> = {
       save: "Guardar",
       saving: "Guardando…",
       back: "Atrás",
+      signOut: "Salir",
+      a11yBackToHeadgates: "Volver a compuertas",
+      a11yChangeHeadgate: "Cambiar compuerta",
+      a11ySignOut: "Cerrar sesión",
+    },
+    brand: {
+      waterLog: "REGISTRO DE AGUA TUXEDO",
     },
     pin: {
       title: "Ingresa tu PIN",
@@ -205,6 +241,8 @@ export const LABELS: Record<Lang, Labels> = {
       unlock: "Desbloquear",
       forgot: "¿Olvidaste tu PIN? Pregúntale al supervisor.",
       genericError: "Algo salió mal. Inténtalo de nuevo.",
+      a11yPin: "PIN",
+      a11yPinEntry: "Entrada de PIN — toca para enfocar",
     },
     headgates: {
       title: "Compuertas",
@@ -216,13 +254,18 @@ export const LABELS: Record<Lang, Labels> = {
       pullToRefresh: "Jala hacia abajo para actualizar la lista",
       thresholdHigh: "Alto",
       thresholdLow: "Bajo",
+      refresh: "Actualizar",
+      refreshing: "Verificando…",
+      loadError: "No se pudieron cargar las compuertas. Jala para intentar de nuevo.",
     },
     log: {
       title: "Registrar lectura",
       measurement: "Medición",
+      unit: "Unidad",
       timestamp: "Hora",
       loggedNow: "Registrando ahora",
       notes: "Notas",
+      notesOptional: "opcional",
       notesPlaceholder:
         "¿Algo que el supervisor deba saber sobre esta lectura?",
       notesVisibility: "Visible solo para administradores",