feat: add age verification endpoints (0.4.1)

[portal-wheatley]

Changes

Adds age verification support to the Java SDK, matching the TypeScript SDK (portal-rest 0.4.1).

New

• VerificationSessionResponse model — session_id, session_url, ephemeral_npub, expires_at, stream_id
• VerificationSession wrapper — holds session info + AsyncOperation<CashuResponseStatus> (same pattern as other composite responses)
• createVerificationSession(relayUrls?) — creates a session and automatically starts listening for the verification token. Returns VerificationSession
• requestVerificationToken(recipientKey, subkeys) — requests a token from a user who already holds one (mobile app flow). Returns AsyncOperation<CashuResponseStatus>

Version bump

0.4.0 → 0.4.1

Usage

VerificationSession session = client.createVerificationSession();
System.out.println("Redirect user to: " + session.session.session_url);

CashuResponseStatus result = client.pollUntilComplete(
    session.operation, new PollOptions(1000, 300_000)
);
if (result.status.equals("success")) {
    System.out.println("Verified! Token: " + result.token);
}

Build

✅ ./gradlew compileJava — BUILD SUCCESSFUL