fix(api-client): generalize 401 redirect from /account/* to all 4 personas

Yesterday's redirectIfCustomerAreaUnauthorized was scoped to /account/*
only. Admin, store, and merchant pages still hit the same UX gap when
an AJAX call returned 401 on token expiry: apiClient cleared tokens
and threw, leaving the page in a broken state with whatever generic
error UI the caller had wired up — no redirect, no `?next=` round-trip,
identical bug to the customer flicker we fixed in `b04b36a2` /
`6564f138`.

Rename and dispatch by path:
  - /account/*     (not /account/login)         → /account/login?next=…
  - /admin/*       (not /admin/login)           → /admin/login?next=…
  - /merchants/*   (not /merchants/login)       → /merchants/login?next=…
  - /store/{code}/* (not /store/{code}/login)   → /store/{code}/login?next=…
  - anything else                               → return false (caller throws)

Store paths include the per-store code, so the helper does a small regex
to extract `{code}` from the current pathname and builds the persona's
login URL with the right prefix.

All three 401 handlers in apiClient (request, requestFormData, getBlob)
already wrap this with the `return new Promise(() => {})` pattern from
6564f138, so the caller's `.finally(() => loading = false)` doesn't fire
before navigation completes — kills the wrong-state UI flash on every
persona, not just customer.

Login pages updated to honour `?next=` precedence over the existing
`*_last_visited_page` localStorage fallback, with persona-specific
safety checks (must start with /admin/, /merchants/, /store/{code}/
respectively; must not be a login or onboarding URL). The store login
also normalises the basePath because the store-code path prefix can
flip between subdomain (/store/{code}/...) and dev/path-based
(/platforms/{platform}/store/{code}/...) modes.

Customer login already honoured `?next=` from bbb481aa; left unchanged.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/modules/tenancy/static/store/js/login.js

@@ -157,18 +157,33 @@ function storeLogin() {
                     ? `/platforms/${platformCode}/store/${this.storeCode}`
                     : `/store/${this.storeCode}`;
 
-                // Check for last visited page (saved before logout)
+                // Decide where to land after login. Precedence:
+                //   1. ?next=<path>  — set by apiClient on 401 mid-session;
+                //      must be a /store/{code}/... URL that doesn't loop back
+                //      to login or onboarding.
+                //   2. store_last_visited_page localStorage — fallback for
+                //      organic logins (preserves the store-relative sub-path
+                //      even if the basePath prefix changed, e.g. domain swap).
+                //   3. {basePath}/dashboard — last-resort default.
+                const nextParam = new URLSearchParams(window.location.search).get('next');
                 const lastPage = localStorage.getItem('store_last_visited_page');
-                let redirectTo = `${basePath}/dashboard`;
+                const isSafeStoreUrl = (u) =>
+                    u && u.includes(`/store/${this.storeCode}/`) &&
+                    !u.includes('/login') && !u.includes('/onboarding');
 
-                if (lastPage && !lastPage.includes('/login') && !lastPage.includes('/onboarding')) {
-                    // Extract the store-relative path (strip any existing prefix)
+                let redirectTo = `${basePath}/dashboard`;
+                if (isSafeStoreUrl(nextParam)) {
+                    redirectTo = nextParam;
+                } else if (lastPage && !lastPage.includes('/login') && !lastPage.includes('/onboarding')) {
+                    // Preserve only the store-relative sub-path; basePath
+                    // may have changed (subdomain ↔ /platforms/... etc.)
                     const storePathMatch = lastPage.match(/\/store\/[^/]+(\/.*)/);
                     if (storePathMatch) {
                         redirectTo = `${basePath}${storePathMatch[1]}`;
                     }
                 }
 
+                storeLoginLog.info('next param:', nextParam);
                 storeLoginLog.info('Last visited page:', lastPage);
                 storeLoginLog.info('Redirecting to:', redirectTo);