onu: info/stats sub-tab with CPE lease health + OUI vendor

Adds an ONU info page and splits the ONU tab into two sub-tabs (Info / stats,
Fleet & upgrade). The ONU tab now lands on Info; campaign/verify keep the
Fleet sub-tab lit.

ONU info page (#view-onu-info): master-detail over the already-loaded fleet
(search + status filter, no new bulk fetch). Per-ONU detail shows identity,
link/optical + FEC (read from the merged ONU-STATE), firmware, and a CPE card.

CPE (customer router):
- McmsClient.getCpe — GET /api/cpe/onu/<id>/ (unversioned, [status,doc] tuple).
- src/cpe.js (pure, shared): summarizeCpe + leaseHealth. Renewal rule —
  <50% of the lease remaining => "renewal overdue" (amber), past end =>
  expired. v4 expiry = DHCP "Remove Time"; v6 spans Last Success ->
  Preferred Lifetime (T1 midpoint), with Prefix Delegation surfaced.
- api:getOnuCpe (main.js + web/server.js, exposed in both bridges).

OUI vendor (src/oui.js, pure, shared): lazy fetch of the IEEE oui.csv,
prefix->org map, cached in memory ~30 days + best-effort to disk
(PFW_CACHE_DIR / temp; PrivateTmp makes /tmp writable). Resolved server-side
in getOnuCpe; every failure degrades to "unknown OUI". CPE itself is not
TTL-cached (lease must be live); only the OUI list is.

Dashboard abnormal Rx/Tx rows are now clickable -> deep-link to that ONU's
info page (showListModal gained per-item onClick).

Docs: CLAUDE.md §17 + IPC table + intro; README.

Verified: node --check; cpe.js/oui.js unit-tested (15/15: lease ok/warn/
expired/unknown + 50% boundary, v6 prefix parse, OUI quoted-CSV parse +
lookup); ONU info page + CPE card rendered offscreen over HTTP.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/public/api-web.js

@@ -147,6 +147,7 @@
     listFleet: (o) => postJSON('listFleet', o),
     fetchStates: (o) => streamJSON('fetchStates', o, 'states'),
     getOnuConfig: (o) => postJSON('getOnuConfig', o),
+    getOnuCpe: (o) => postJSON('getOnuCpe', o),
     listOnuFirmware: () => postJSON('listOnuFirmware', {}),
     uploadFirmware: async () => {
       const file = await pickFile('.bin');