docs: document EPSS Priority Signal in Reading the Output and HTML Report guides

[RohithPariki]

Problem

With the introduction of the EPSS Priority Signal feature (#1067 / #1066), findings are now classified into actionable priority tiers (\ix_now, \ix_soon, \monitor, \low_priority) combining CVSS severity and EPSS exploitation percentiles. While this was added to \website/docs/cli-reference.md, other key documentation guides were not updated:

1. **\website/docs/reading-output.md**:

   • The compact mode section does not explain the inline [⚡ Fix Now]\ badge.
   • The verbose output findings section does not describe the \EPSS\ and \EPSS Priority\ table columns or how developers should interpret them during triage.

2. **\website/docs/html-report.md**:

   • Does not mention the EPSS Priority column, interactive four-tier legend, or detail badges displaying exploitation percentiles.

Proposed Solution

• Update \website/docs/reading-output.md\ to document how the EPSS Priority Signal appears in compact mode ([⚡ Fix Now]) and verbose mode (\EPSS Priority\ column), and how to use it in the triage workflow.
• Update \website/docs/html-report.md\ to list the EPSS Priority column, detail badges, and interactive legend under what the report shows.