Fix daily dashboard refresh blocked by late market-data feeds

[LEO0331]

Diagnosis

Failed scheduled run #37 rejected its snapshot because all 20 tracked tickers had 260 historical closes through October 12 while the readiness gate required the October 13 NYSE session. Stooq requests failed or timed out; Yahoo Finance was one session behind. The 20 blockers are correctly enforced by evaluateDemoReadiness.

Change

• Schedule the daily snapshot for 12:17 UTC (08:17 EDT / 07:17 EST) rather than 22:17 UTC, giving the previous US market session's daily bars overnight to settle before validation.
• Add regression coverage for the scheduled market session across daylight saving changes and the weekend.
• Preserve strict per-ticker freshness checks and unchanged last-known-good snapshot semantics. No stale data is disguised as fresh.

Validation / limitations

• Inspected all 20 failures in the GitHub Actions job logs.
• Updated only the scheduled workflow and its workflow timing test.
• CI should run the test suite when this PR is opened. Live provider recovery cannot be guaranteed; persistent vendor outages must still fail closed.
• This changes publication timing: the dashboard updates after the prior US session overnight, rather than shortly after that session closes.