fix: car-sales tutorial — match actual evo-sdk API

[thepastaclaw]

Adds a corrected version of the Car Sales tutorial that compiles against @dashevo/evo-sdk@3.1.0-dev.1.

Changes from original tutorial

API	Tutorial (broken)	Fixed
contracts.publish()	{ identityId, documentSchemas, privateKeyWif }	{ dataContract: DataContract, identityKey, signer: IdentitySigner }
documents.create()	{ contractId, documentType, document: {...} }	{ document: new Document({...}), identityKey, signer }
documents.query()	contractId, documentType	dataContractId, documentTypeName
documents.replace()	{ documentId, document: {...} }	Fetch existing doc, mutate .properties, bump .revision
contract.getId()	method call	contract.id (property getter)
doc.getData()	method call	doc.properties
identity.getPublicKeys()	method call	identity.publicKeys (property)

npx tsc --noEmit passes with zero errors.

Resolves #3

[thepastaclaw]

✅ Live Testnet Run — All Steps Passed

Ran the car sales tutorial end-to-end on testnet with identity HHjmkbcwqFzToaoyvQcP45JZro7PoczAv7Nii57uYPX1.

Published: FZiA9xeDYZ47AmRm5aHea9X94kXNqBDds2aS2gu3T8cw
Listing created!
Query: 1 results
  Toyota Camry $22500 available
Updated to sold!
Review created!
Reviews: 1
  rating: 5 Great!

=== CAR SALES: ALL STEPS PASSED ===

Additional issues discovered during live testing

These are NOT just API name mismatches — they would prevent any tutorial from working even with the correct method signatures:

1. Schema properties require position fields — DPP requires each property to have a position: N field. The tutorials omit this entirely.
2. Indexed string properties need maxLength <= 63 — The tutorial uses maxLength: 64 for indexed fields like make and status, but the platform rejects values >63 for indexed strings.
3. Index sort direction only supports asc — The tutorial uses orderBy: [["rating", "desc"]] but the platform only accepts asc in index definitions.
4. identityNonce needs +1 — sdk.identities.nonce() returns the last used nonce; DataContract constructor needs the next one (nonce + 1n).
5. Integer properties return as bigint — When queried back, integer fields come as bigint. When passing them back to replace(), they must be converted to number or the platform rejects them with "not of type integer".