fix(sec): poll latest filings every ten seconds

[daniel3303]

Summary

Reduce the default SEC Latest Filings discovery delay from 60 seconds to a ten-second minimum after completed scrape cycles.

Code changes

• Set the recent-feed poll and SEC worker sleep defaults to ten seconds.
• Add regression tests for both defaults.
• Document the distinction between discovery cadence, processing cadence, and end-to-end availability.
• Keep all EDGAR traffic behind the existing shared five-requests-per-second limiter.

Verification

• Release solution build passed.
• 4,467 unit tests passed.
• 32 focused tests passed after documentation fixes.
• CSharpier and git diff checks passed.
• Independent audit passed with no blocking or high-confidence findings.