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/features/dashboard.mdx

@@ -169,7 +169,7 @@ A **Clear All Notifications** button is anchored at the bottom right of the card
 
 The list paginates at eight rows; chevrons and an `N / M` indicator appear in the header when there is more than one page.
 
-Alert rules and severity routing are configured per stack in **Settings · Notifications**. See [Alerts and notifications](/features/alerts-notifications) for channel setup, per-stack rules, and the routing engine.
+Alert rules and severity routing are configured per stack in **Settings · Notifications · Channels**. See [Alerts and notifications](/features/alerts-notifications) for channel setup, per-stack rules, and the routing engine.
 
 ## How health is derived
 
@@ -226,6 +226,6 @@ When you switch the active node from the node switcher, the dashboard resets eve
     Critical can fire on RAM, disk, or the combination of any exited container with an unread error alert, not only on CPU. Read the reasons line right under the meta line; it lists every signal pushing the state up. Common cases: RAM at or above 90% from an oversized service, disk at or above 90% from runaway log retention, or a crashed container that no one has acknowledged in the alerts panel.
   </Accordion>
   <Accordion title="The dashboard feels sluggish on a large deployment">
-    Toggle **Developer mode** under **Settings · System**. Both dashboard endpoints then emit a `[Dashboard:debug]` line in the Sencho container logs for every request, reporting elapsed milliseconds and the contextual fields (`nodeId`, row count, `days` window). Use the timings to identify whether the Configuration Status payload or the stack-restarts query is the bottleneck. Disable developer mode when you are done to keep the log volume manageable.
+    Toggle **Developer mode** under **Settings · Operations · Developer Diagnostics**. Both dashboard endpoints then emit a `[Dashboard:debug]` line in the Sencho container logs for every request, reporting elapsed milliseconds and the contextual fields (`nodeId`, row count, `days` window). Use the timings to identify whether the Configuration Status payload or the stack-restarts query is the bottleneck. Disable developer mode when you are done to keep the log volume manageable.
   </Accordion>
 </AccordionGroup>