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/tariff.md

@@ -10,7 +10,7 @@ status: open
 
 How a [[parking-session]]'s fee is computed from its duration. A tariff is **admin-composed data,
 not code** — the park owner builds and constantly edits the rate card at runtime (like a
-[[permit]]), in a selectable currency, with **no numbers hard-coded anywhere** and no code change to
+[[subscription]]), in a selectable currency, with **no numbers hard-coded anywhere** and no code change to
 reprice. The computation is **pure and offline** ([[offline-first]]: no network, no clock authority
 beyond the host).
 
@@ -144,9 +144,9 @@ production.
 
 ## Permit holders
 
-A valid [[permit]] bypasses tariff computation entirely for the covered period (subscription
+A valid [[subscription]] bypasses tariff computation entirely for the covered period (subscription
 already paid out-of-band). A permit that has lapsed mid-stay falls back to the transient tariff for
-the uncovered time — an edge case to design with [[permit]].
+the uncovered time — an edge case to design with [[subscription]].
 
 ## Versioning — edits publish immutable, effective-dated versions
 
@@ -198,7 +198,7 @@ Two operator asks extend this engine; both have design pages (not yet built), gr
   slicing a stay at window boundaries while keeping the block ladder + daily cap continuous.
 - **Validation & sponsorship** (merchant comps, coupons, **postpaid B2B** "enter/exit free, bill the
   business monthly") — see [[validation-sponsorship]]. A validation is a **typed modifier applied as a
-  signed event** on a transient session, distinct from a [[permit]]; postpaid sponsors accrue a
+  signed event** on a transient session, distinct from a [[subscription]]; postpaid sponsors accrue a
   monthly-invoiced liability derivable from the chain.
 
 ## Open