Separate 'run date' and 'run upload date'

Summary

The submission CLI currently conflates two distinct concepts under a single "date": the date a benchmark run actually happened, and the date a run/submission was uploaded to the API. We should treat these as two separate fields with different semantics.

Background

Today, runs create and submissions create-local each compute a single timestamp for a run in different, inconsistent ways (one derives it from the benchmark's own log when available and falls back to "now"; the other always uses "now"). That timestamp is then used to populate the run_date field, which can end up not reflecting when the benchmark was actually executed.

Proposal

Introduce two clearly separate fields:

1. Run date — the date the benchmark run actually started/completed. This must come from the benchmark's own output log (e.g. result_summary.json). It should never be inferred or defaulted by the CLI.
   • If the run log does not contain this information, the CLI should error out rather than silently substituting a fallback value (like the current upload time). This is a signal that the benchmark output itself is missing required data.
2. Run upload date — the date the run/submission was uploaded via the CLI. This can simply be the current timestamp at upload time, since that's genuinely what it represents.

Notes

• The exact field/schema for how "run date" is emitted by the benchmark log is still being finalized, so this issue is to track the requirement, not to implement it yet.
• Once the benchmark output format is finalized, the CLI's run-parsing logic should be updated to read run date strictly from the log and fail fast if it's absent, and to record upload date as a separate, independent field.

This issue was created by Claude.

Start by tracing the runs create and submissions create-local command paths and their run-parsing logic. Wait for the benchmark output schema to be finalized, then verify that run date is read only from the log, upload date is recorded independently, and missing run-date data produces an error.