feat(settings): reorganize the settings hub into domain groups (#1321)

* refactor(settings): split System Limits and regroup the hub

System Limits had grown into a grab-bag of host alert thresholds, Docker
cleanup, and mesh data-plane controls under one mislabeled section. Split it
into Host Alerts, Docker & Storage, and Fleet Mesh, and split Developer into
Developer Diagnostics and Data Retention. Reorganize the sidebar into ten
domain groups: Personal, Access, Infrastructure, Monitoring, Notifications,
Automation, Organization, Security, Operations, Help.

Each section now saves only its own keys, so a concurrent edit in one section
no longer clobbers another. Data Retention sends the audit-log window only on
a paid plan, matching the field's existing visibility, so a Community save no
longer fails on a key the operator cannot set. NumberChip moves to a shared
module and the toggle reuses the existing shared component. The /settings API
is unchanged.

* test(settings): cover registry structure and per-section save payloads

Add structural invariants for the ten-group registry (every item maps to a
real group, ids are unique, the System Limits and Developer splits land in the
right groups with the right gates, renamed labels and the Registries paid gate
hold) and per-section payload tests asserting each split section patches only
its own keys, including the Community path where Data Retention omits the paid
audit-log key.

* docs(settings): document the regrouped settings hub

Rewrite the settings reference for the ten-group layout, replace the System
Limits page with Host Alerts, Docker & Storage, and Fleet Mesh, and document
the prune-on-update, reclaimable-space banner, and mesh auto-recreate settings
that were previously undocumented. Update the Settings navigation breadcrumbs
across the feature docs and refresh the affected screenshots.

* fix(settings): show Access sections as instance-global, not operator-scoped

License, Users, SSO, and API Tokens are instance-global settings but the
masthead scope label rendered them as operator-scoped because it keyed off the
old Identity group. Only Personal sections (account, appearance) are
operator/browser-scoped now; everything else reads as global.

Also add a compile-time exhaustiveness guard to the section switch so a future
SectionId added without a matching case fails the build instead of silently
rendering a blank panel.

* docs(settings): remap remaining settings breadcrumbs to the new groups

Update the navigation breadcrumbs that still pointed at the removed Identity,
Alerts, and Advanced groups: API Tokens and Users now sit under Access, Webhooks
under Automation, Labels under Organization, App Store under Infrastructure,
Appearance under Personal, and scan policies under Security > Vulnerability
Scanning. Correct the settings reference scope note so Access reads as global.

* docs(settings): remap renamed-section breadcrumbs across feature docs

Sweep every feature, operations, getting-started, and reference page for
navigation paths that still named the renamed settings sections, and point them
at the current ones: Security becomes Security > Vulnerability Scanning,
Notifications becomes Notifications > Channels, Routing becomes Notifications >
Notification Routing, and Developer becomes Operations > Developer Diagnostics
(with its retention windows under Operations > Data Retention). App Store moves
under Infrastructure and the four-group overview in the getting-started intro is
rewritten to the ten groups. Separators each page already used are preserved.

docs/operations/two-factor-admin.mdx

@@ -48,7 +48,7 @@ The command respects the container's `DATA_DIR`, so it always acts on the same S
 This is one of several host-level recovery commands. See [Emergency command-line recovery](/operations/emergency-cli) for the full set, including password reset, creating an emergency admin, and disabling a broken SSO provider.
 
 <Note>
-  Enabling **Developer Mode** under **Settings · Developer** surfaces additional `[MFA:diag]` lines in the backend logs. They are helpful when investigating a 2FA support ticket and can be turned off again once the issue is resolved.
+  Enabling **Developer Mode** under **Settings · Operations · Developer Diagnostics** surfaces additional `[MFA:diag]` lines in the backend logs. They are helpful when investigating a 2FA support ticket and can be turned off again once the issue is resolved.
 </Note>
 
 ## SSO and 2FA: two independent toggles