Add 12 missing canonical examples

[nficano]

TS SDK ships 22 canonical examples; Java SDK has 10. Add Java equivalents (under examples/ or samples/) for:

• ack-backpressure, delegate (end-to-end), express (replace w/ Spring Boot if not present), fastify (replace w/ Jakarta), lease-violation, progress, resume, stdio, subscribe, tracing, vendor-extensions, bun (or document as N/A)

Each example should be a small runnable Gradle/Maven module with its own README. Source references at /Users/nficano/code/arpc/typescript-sdk/examples/<name>/.

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Audit reference: ARCP SDK Audit v1.1 (2026-05-19)