feat: add deterministic text_retrieve workload across local execution, routing, and validation

[Exohayvan]

Objective

Add a deterministic text_retrieve workload to the existing local-only prototype so the mesh can execute a realistic AI-adjacent ranking task end-to-end (runner -> scheduler -> validation -> ledger) while keeping the change local, testable, and auditable.

This matters because it expands useful work types without introducing networking, rewards, or production infrastructure changes, and exercises the same local transport/validation contracts already in place.

What changed

• Added text_retrieve support in LocalRunner with strict payload validation, deterministic token extraction, overlap scoring, stable tie-break sorting, and deterministic output shaping.
• Wired text_retrieve into validation so expected results are recomputed locally and mismatches are rejected (including malformed payloads and incorrect contribution units).
• Included text_retrieve in default local capabilities so manifest default nodes can advertise and accept the new job type.
• Added a text_retrieve job to the default local batch example and updated README docs to document required fields, scoring semantics, and failure behavior.
• Updated manifest/capability/scheduler tests to account for the new workload and keep routing assertions aligned.
• Added coverage in runner, validation, scheduler, simulation, CLI, node service, and related tests for success paths, malformed payloads, stable ordering, and accounting.

Validation

• Ran the local unit test suite: PYTHONDONTWRITEBYTECODE=1 PYTHONPATH=src python3 -m unittest discover -s tests -v (310 tests, all passed).
• Ran a local flow smoke test: run-local-flow --manifest examples/local-batch.json --output-dir <tmp-output-dir> and confirmed the added workload flowed end-to-end with processed_assignment_count=6, receipt_count=6, and matching ledger total contribution units.
• Ran audit-local-flow --output-dir <tmp-output-dir> and confirmed flow artifacts validated successfully with ok: true and consistent counts.

Safety notes

• No force push used.
• No hard reset used.
• Local automation paths are not published in this PR body.

[Exohayvan]

Automated conflicting-PR triage refreshed this branch because the PR change is still relevant. Review log path intentionally redacted.