Implements the wiki design in packages/db + packages/shared.
Event split: rename events -> ledger_events (signed business ledger) and add
device_events (unsigned telemetry). ledger_events gains a signed JSON payload
(amount/tariffVersionId/sessionRef/tender…) + keyId; canonicalize() includes
the payload via sorted-key serialization so business data is tamper-evident.
Raw Dingtian input now writes device_events, not a signed input_received.
New tables: tariffs + immutable tariff_versions (composable/versioned, currency
+ FX-ready), permits (+ permit_credentials, permit_plates; maxConcurrent default
1), blocklist, sessions (rebuildable projection cache — not a source of truth).
shared: split ParkingEvent/Type into LedgerEvent/LedgerEventType + DeviceEventKind;
add LedgerPayload, Tender, TariffStructure/TariffBlock.
Regenerated a single baseline migration (no production chain data existed).
Verified: chain appends + verifyChain ok; tampering a payment payload breaks
the signature. Full repo builds (5/5).
