feat(subscription): rename permit→subscription + monthly pricing

The "permit/lejet" feature is really a subscription. Full rename of the
mutable master data, plus a recurring monthly price.

- DB (migration 0004, data-preserving ALTER RENAME): permits→subscriptions,
  permit_credentials/_plates→subscription_*, sessions.permit_id→subscription_id.
- Pricing: per-subscription priceMinor + period(monthly) + currency, with a
  site default (site_config.subscription_monthly_price_minor) pre-filling the form.
- Server: subscription-flow.ts (SubscriptionFlow), routes/subscriptions.ts
  (/api/subscriptions). Web: SubscriptionManager, route, i18n (sq Abonimet/en).
- The signed ledger `permitId` payload is intentionally kept — immutable
  hash-chained history; renaming it would break verification of past events.

Deferred (wiki notes): fee collection into the ledger/shift (a shift-attributed
payment), LPR/ANPR plate source, time-of-day access windows (overnight subscriber).

Also carries the device-footer UI surface (api DeviceStatus, router mount,
i18n devices) due to shared-file overlap with the preceding footer commit.

Verified end-to-end on a fresh DB and migration on a live-DB copy (sessions
preserved). Live DB migrated. Full monorepo builds clean.

Claude-Session: https://claude.ai/code/session_01Xcm6ikLgGoCxxHrxtjkk5V

wiki/concepts/capacity-occupancy.md

@@ -18,7 +18,7 @@ editable and drifts; the chain is the truth). Spaces-free = `capacity − occupa
 
 - **`capacity`** is admin-set per site (and per **zone/level** if the lot has sections — model a
   `zone` on capacity + on the entry so multi-level is a later addition, not a rewrite).
-- Permit concurrency (`maxConcurrent`, see [[permit]]) is the same kind of fold, scoped to one
+- Permit concurrency (`maxConcurrent`, see [[subscription]]) is the same kind of fold, scoped to one
   permit's open sessions.
 
 ## Full → refuse entry + FULL sign