feat(water-log): cycle 6 — worker sub-PWA at /water scope

Same-origin sub-PWA for Tuxedo field workers, fully isolated from the
main Route Commerce PWA.

- public/manifest-field.json: Tuxedo-branded manifest, start_url=/water,
  scope=/water, themeColor=#14532d, no Route Commerce branding
- public/sw-field.js: scoped SW with field-shell-v1 + field-data-v1
  caches (never touches main app's rc-shell-v* / rc-data-v*). Skips
  any request outside /water scope. Two-cache strategy: shell
  cache-first + /api/water stale-while-revalidate.
- src/app/water/layout.tsx: child layout overrides root metadata
  (manifest, themeColor, applicationName, appleWebApp.title) and
  mounts the field SW registration + install prompt.
- src/components/pwa/FieldSWRegistration.tsx: registers /sw-field.js
  with scope=/water. Module-scoped registered flag prevents strict-
  mode double-registration.
- src/components/pwa/FieldInstallPrompt.tsx: sibling of InstallPrompt,
  forest-green #1a4d2e theming, fires after 4s dwell. Captures
  display-mode:standalone AND navigator.standalone for iOS.

No conflict with the main app PWA: PWAInstallPrompt is mounted only
under /admin/layout.tsx, so /water routes only see FieldInstallPrompt.

Tuxedo-only by design (matches existing /water single-tenant hardcode).

public/manifest-field.json

@@ -0,0 +1,17 @@
+{
+  "name": "Water Log — Tuxedo",
+  "short_name": "Water Log",
+  "description": "Field access for Tuxedo water + time tracking",
+  "start_url": "/water",
+  "scope": "/water",
+  "display": "standalone",
+  "background_color": "#f2f2f7",
+  "theme_color": "#14532d",
+  "orientation": "portrait-primary",
+  "icons": [
+    { "src": "/icons/icon-192x192.png", "sizes": "192x192", "type": "image/png", "purpose": "any" },
+    { "src": "/icons/icon-512x512.png", "sizes": "512x512", "type": "image/png", "purpose": "any" },
+    { "src": "/icons/icon-maskable-512x512.png", "sizes": "512x512", "type": "image/png", "purpose": "maskable" }
+  ],
+  "categories": ["productivity", "utilities"]
+}

public/sw-field.js

@@ -0,0 +1,129 @@
+// public/sw-field.js — Tuxedo field-worker service worker.
+//
+// Cycle 6 sub-PWA, scoped to /water. Tighter cache strategy than
+// the main shell SW because:
+//   - The field app is a thin surface (PIN, headgate list, log form,
+//     time tab). Few async chunks; mostly static + the latest data
+//     snapshot.
+//   - "Offline" here means "still see the cached PIN screen + headgate
+//     list" — water entry without connectivity is a degraded but
+//     non-blocking experience (the form queue handles drafts).
+//
+// Cache names are deliberately prefixed with `field-` so they never
+// collide with the main `rc-shell-v*` / `rc-data-v*` caches.
+
+const SHELL_CACHE = "field-shell-v1";
+const DATA_CACHE = "field-data-v1";
+const OFFLINE_URL = "/offline.html";
+
+const SHELL_ASSETS = [
+  "/water",
+  "/manifest-field.json",
+  "/favicon.svg",
+  "/og-default.svg",
+  "/offline.html",
+  "/icons/icon-192x192.png",
+  "/icons/icon-512x512.png",
+];
+
+self.addEventListener("install", (event) => {
+  event.waitUntil(
+    caches.open(SHELL_CACHE).then((cache) => cache.addAll(SHELL_ASSETS))
+  );
+  self.skipWaiting();
+});
+
+self.addEventListener("activate", (event) => {
+  // Only manage field-* caches — never touch the main app's caches.
+  event.waitUntil(
+    Promise.all([
+      caches.keys().then((cacheNames) => {
+        const toDelete = [];
+        for (const name of cacheNames) {
+          if (
+            name !== SHELL_CACHE &&
+            name !== DATA_CACHE &&
+            name.startsWith("field-")
+          ) {
+            toDelete.push(caches.delete(name));
+          }
+        }
+        return Promise.all(toDelete);
+      }),
+      self.clients.claim(),
+    ])
+  );
+});
+
+self.addEventListener("fetch", (event) => {
+  const req = event.request;
+  if (req.method !== "GET") return;
+  const url = new URL(req.url);
+  if (url.origin !== self.location.origin) return;
+
+  // Out-of-scope requests: skip (let the main app SW handle them
+  // if it's installed for that scope; fall through to network).
+  if (!url.pathname.startsWith("/water")) return;
+
+  // Navigations → network-first, fall back to cache, fall back to offline page.
+  if (req.mode === "navigate") {
+    event.respondWith(
+      fetch(req)
+        .then((res) => {
+          const clone = res.clone();
+          caches.open(SHELL_CACHE).then((cache) => cache.put(req, clone));
+          return res;
+        })
+        .catch(() =>
+          caches.match(req).then(
+            (cached) => cached ?? caches.match(OFFLINE_URL),
+          ),
+        ),
+    );
+    return;
+  }
+
+  // Static assets → cache-first
+  if (
+    url.pathname.startsWith("/_next/static/") ||
+    url.pathname.startsWith("/icons/") ||
+    url.pathname.endsWith(".svg") ||
+    url.pathname.endsWith(".woff2")
+  ) {
+    event.respondWith(
+      caches.match(req).then((cached) => {
+        if (cached) return cached;
+        return fetch(req).then((res) => {
+          const clone = res.clone();
+          if (res.status === 200) {
+            caches.open(SHELL_CACHE).then((cache) => cache.put(req, clone));
+          }
+          return res;
+        });
+      }),
+    );
+    return;
+  }
+
+  // /api/water* GETs → stale-while-revalidate (so the headgate list
+  // and worker availability can hydrate from cache while we re-fetch).
+  if (url.pathname.startsWith("/api/water")) {
+    event.respondWith(
+      caches.open(DATA_CACHE).then((cache) =>
+        cache.match(req).then((cached) => {
+          const network = fetch(req)
+            .then((res) => {
+              if (res.status === 200) cache.put(req, res.clone());
+              return res;
+            })
+            .catch(() => cached);
+          return cached ?? network;
+        }),
+      ),
+    );
+    return;
+  }
+
+  // Default: try network, fall back to cache.
+  event.respondWith(fetch(req).catch(() => caches.match(req)));
+});