[ubcodes]

Summary

• Cuts SDK 1.5.0 (pom.xml + README Maven/Gradle coords) so the published coordinate matches work already on main.
• Renames changelog ## Unreleased — Core 0.15.4 → ## 1.5.0 — Core 0.15.4 (error catalogue, multiSearch, list ledgers/balances/transactions, listByBalanceId).

This release includes Core 0.15.4 alignment already merged:

• Full error_detail.code catalogue (TXN_ALREADY_REFUNDED, BAL_NOT_FOUND, …)
• POST /multi-search
• GET list ledgers, balances, and transactions (ListOptions)
• balanceMonitor().listByBalanceId

After merge (do not do this on the PR branch)

• Tag v1.5.0 on main so .github/workflows/publish.yml can run (on: push: tags: v*.*.*).
• Do not publish to Maven Central from this PR; staging waits for the tag plus a manual Portal publish.

Test plan

• Confirm pom.xml version is 1.5.0 and README install snippets match
• Confirm CHANGELOG heading is ## 1.5.0 — Core 0.15.4 and all Unreleased bullets remain
• CI: compile, unit tests, Javadoc on JDK 17 and 21
• Local: mvn -o -q clean test passed on this branch (stale target/ duplicate class files required a clean)
• After merge: tag v1.5.0 only when ready to stage Central; verify tag matches pom version