Add public creator-review example for Task Validation V2

[signerless]

Summary

Add a root-level public example that demonstrates the reviewed settlement flow for Task Validation V2.

Why

#1518 now has protocol, runtime, SDK, and umbrella docs work either merged or in review, but the umbrella examples still do not show the end-to-end public reviewed path. examples/README.md already calls out this gap.

Scope

• create or document a runnable public example for a task configured with manual validation / creator review
• show the lifecycle end-to-end: configure validation, submit result, accept or reject result, final settlement
• keep the example on public surfaces only: umbrella docs/examples plus SDK/runtime entrypoints
• link the example from root docs and examples navigation

Acceptance Criteria

• the root repo contains a discoverable example or walkthrough for public reviewed task settlement
• the example covers task creation/configuration for creator review or manual validation
• the example covers worker submission
• the example covers creator acceptance
• the example either covers creator rejection or clearly documents the rejection path
• examples/README.md and relevant root docs link to the example
• public example validation passes, or the docs explain clearly why the example is documentation-only

References

• Task Validation V2: separate submission from settlement for review-based and externally verified tasks #1518
• docs: surface Task Validation V2 entrypoints in umbrella docs #1522
• docs: document Task Validation V2 runtime flow agenc-core#36
• docs: add Task Validation V2 helper docs to SDK agenc-sdk#27