feat(devices): pair-a-device card replaces the pending registration list

The Devices page's Pending Device Registrations section (Approve/Reject
cards broadcast to every account) is replaced by an always-visible Pair
a Device field: type the 6-digit code shown on the registering e-reader,
a templ-rendered confirm card shows what will be bound, and confirming
claims the device to the signed-in account.

Rendering ownership (AGENTS.md): the confirm card and every lookup
outcome are templ partials (PairingLookupResult) swapped by htmx from a
new SSR route POST /devices/pairing/lookup — the server decides what UI
looks like, no JSON-built HTML. Errors render as content because htmx
only swaps 2xx bodies (the route is web-only; the JSON API keeps real
status codes), and one delegated htmx:responseError listener in
device-management.ts toasts the non-swap failure path.

The claim confirm button posts straight to /api/devices/claim; success
comes back as HX-Refresh (same pattern as token regeneration), so the
page reloads into the paired state. No new TS module is needed — plain
htmx attributes drive the whole flow.

Ride-alongs: the Add New Device modal loses the device-type select and
the kobo manual form (its post-register UX depended on the broadcast
list and silently produced an unclaimable registration; native Kobo
sync is still server-side-only and will get its own pairing UX when it
lands) — the modal is now a single Connect-a-KOReader-Device guide with
the pairing steps. PendingRegistrationData, convertPending, and the
pending plumbing in the page handler are gone with the section.
ui-controls.md glossary and tests/ui COVERAGE.md updated in the same
commit as the control rename, per the drift gates.

docs/developer/ui-controls.md

@@ -182,9 +182,13 @@ label: Filters
 where: All Books / Podcasts page → toolbar
 does: Opens the filter drawer for building and applying rules.
 
-label: Register Device
-where: Devices page
-does: Submits a device registration request for the pending-approval flow.
+label: Find device
+where: Devices page → Pair a Device
+does: Looks up the pairing code shown on the registering e-reader and renders the confirm card.
+
+label: Pair device
+where: Devices page → Pair a Device → confirm card
+does: Binds the device behind the pairing code to the signed-in account.
 
 label: Download All
 where: Podcast page → episodes area