Verify tests pass and derivation correctness

[variablefate]

Context

After fixing the build (#1), all existing tests need to be verified against the current nostr-sdk-swift 0.44.x dependency. The package was last iterated on before the platform issue was discovered, so test results are unverified.

What to verify

1. All existing tests pass (NostrPasskeyTests.swift)
2. Default derivation produces deterministic keys (same passkey + same salt = same key)
3. Indexed derivation produces distinct keys per index
4. Passphrase derivation produces deterministic keys
5. Cross-platform test vector (from commit 1cf3987) still holds
6. NIP-19 encoding/decoding round-trips correctly

Depends on

• Fix platform manifest — package cannot build #1 (build fix)