refactor: Replace `jsonwebtoken` with `jose`

[koistya]

• Use an RSA (asymmetric) key pair for JWT signing/verification (RSASSA-PKCS1-v1_5)
• These key pair can be generated using yarn generate:keys --env <envName> command
• Remove JWT_SECRET passphrase in favor of PUBLIC_KEY, PRIVATE_KEY
• Replace jsonwebtoken with jose as a more modern alternative, supporting JWK keys

BREAKING CHANGE:

If you're using createIdToken, verifyIdToToken helper methods, you need to add await:

// BEFORE
createIdToken(...)
verifyIdToken(...)
createState(...)
verifyState(...)

// AFTER
await createIdToken(...)
await verifyIdToken(...)
await createState(...)
await verifyState(...)