fix(ui): inject window.FRONTEND_TYPE from server + rename SHOP→STOREFRONT

Server now injects window.FRONTEND_TYPE in all base templates via
get_context_for_frontend(). Both log-config.js and dev-toolbar.js read
this instead of guessing from URL paths, fixing:
- UNKNOWN prefix on merchant pages
- Incorrect detection on custom domains/subdomains in prod

Also adds frontend_type to login page contexts (admin, merchant, store).

Renames all [SHOP] logger prefixes to [STOREFRONT] across 7 files
(storefront-layout.js + 6 storefront templates).

Adds 'merchant' and 'storefront' to log-config.js frontend detection,
log levels, and logger selection.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/templates/storefront/base.html

@@ -349,6 +349,9 @@
 
     {# JavaScript Loading Order (CRITICAL - must be in this order) #}
 
+    {# 0. Frontend type (server-injected, used by log-config and dev-toolbar) #}
+    <script>window.FRONTEND_TYPE = '{{ frontend_type | default("storefront") }}';</script>
+
     {# 1. Log Configuration (must load first) #}
     <script defer src="{{ url_for('static', path='shared/js/log-config.js') }}"></script>