Splits the 755-line monolithic settings page into a tile-based landing hub
and six focused subpages (general, security, email, api, sso, branding),
each with its own form, CSRF scope and POST handler. Each subpage offers
Save / Save & close buttons plus a Cancel/back link to the hub.
Backend (AdminSettingsService, gateways, policies, DB schema) unchanged.
A new settingsSectionMergePost() helper overlays section POSTs onto the
current DB values so partial saves don't wipe unrelated fields (the
service defaults missing keys to 0/empty).
Sub-action files (logo/favicon/tokens/lifecycle) redirect to the matching
subpage, and architecture contracts now check the subpage files instead
of the removed monolithic index.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
