fix: redact persisted manifests from job details

[homerquan]

Motivation

• The runtime began persisting full unredacted manifests into job records and returning the persisted job map in Monitor.job_details/2, which exposed sensitive manifest contents (metadata, node configs, tool bindings, initial inputs) to API callers.
• The change prevents accidental information disclosure via the monitor/grpc GetJob surface while preserving job metadata required for operator workflows.

Description

• Add a helper public_job/1 that removes the embedded "manifest" key from persisted job maps using Map.drop/2.
• Update Monitor.job_details/2 to return public_job(job) instead of the raw persisted job, preserving manifest_ref and other metadata.
• Add an end-to-end regression test test "job details does not expose persisted embedded manifests" to tests/e2e/monitor_test.exs which persists a job with a synthetic secret-containing manifest and asserts the manifest is not returned while manifest_ref and summary remain available.
• Keep other monitor behavior unchanged (summaries, agents, recent events, sandboxes) so operator-visible data is preserved.

Testing

• Ran mix format on the modified files successfully (lib/mirror_neuron/monitor.ex and tests/e2e/monitor_test.exs).
• Performed a syntax check using elixir to parse the modified files successfully.
• Attempted to run mix deps.get / mix test but it was blocked by the environment (Hex metadata download failed with HTTP 403), so full automated test execution could not complete in this environment.

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Codex Task