Make table page size a configurable setting, not a hardcoded 20

Pagination just landed hardcoded to 20 rows everywhere; add a way to
change that instead of leaving it fixed for every table in the app.

pageSize joins dateFormat/timeFormat on the existing display settings
object (server-side default 20, 5-500 range enforced by the PUT
schema) rather than becoming its own settings section, since it's the
same kind of thing -- an admin-configured, globally-applied display
preference read by every signed-in role via the already-public GET
/api/settings/display endpoint, same as the date/time format already
works.

Renamed the "Date & Time" settings tab/page/route to "Display" (still
just one component, now covering both date/time format and table
pagination) since its scope no longer matches the old name -- kept
Settings.tsx's usual pattern of one page per concern rather than
adding a second, oddly-scoped tab just for one number field.

New web/src/utils/pageSize.ts mirrors utils/date.ts's existing
module-level "set once at startup, read anywhere without prop-
drilling" pattern; usePagination()'s pageSize parameter now defaults
to getPageSize() instead of a literal 20, evaluated fresh on every
call so it picks up a saved change without touching any of the ten
pages already using the hook.

Verified server-side against a temp SQLite DB: pageSize defaults to
20, a partial update sets it without disturbing dateFormat/timeFormat
and vice versa, and it persists across a fresh settings read. Also
checked the default-parameter mechanics directly (re-evaluates the
global value on every call rather than capturing it once, and an
explicit override still wins).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

README.md

@@ -98,17 +98,18 @@ All modules from the original plan are built:
   and has an "Export CSV" button next to it that exports whatever's
   currently sorted/filtered. Tables that can realistically grow large
   (DNS zones/records, IP Addresses, Secrets, Servers, Audit Log, and each
-  integration's device/container/guest/repo/template list) are paginated
-  20 rows at a time — CSV export still covers every sorted/filtered row,
-  not just the current page.
+  integration's device/container/guest/repo/template list) are paginated,
+  20 rows per page by default — adjustable under Settings → Display — and
+  CSV export still covers every sorted/filtered row, not just the current
+  page.
 - **Settings** (admin-only) — notification channels (Gotify, ntfy, SMTP,
   generic webhook) with per-channel test buttons, per-event toggles (DNS
   record added/updated/deleted, daily secret-expiry reminder and daily
   Tailscale key-expiry reminder — both sharing one configurable
   time/timezone), badge-color customization for both DNS
-  providers and integration types, and a date/time display format
-  (date order, 12/24-hour clock) applied consistently to every table in
-  the app.
+  providers and integration types, and a **Display** tab (date order,
+  12/24-hour clock, and rows-per-page for every paginated table) applied
+  consistently across the app.
 
 All six integrations follow the same config-in-UI + encrypted-credentials
 pattern, added (and edited — e.g. to rotate an expired API token without