Rename Traffic Snapshots to PCAP Snapshots and enrich PCAP documentation

[alongir]

Description

Update the documentation to rebrand "Traffic Snapshots" as PCAP Snapshots and enrich the PCAP-related content across multiple pages:

1. Rename "Traffic Snapshots" to "PCAP Snapshots" throughout the docs.
2. Add an intro description at the top of the Snapshots page highlighting the ability to capture retrospective, cluster-wide PCAP filtered by BPF statements, node, and time — all in one click.
3. Add a screenshot of the filter dialog to the Snapshots page.
4. Enrich the PCAP Export section in the Dashboard page with more detail on export capabilities.
5. Add a brief PCAP Snapshots description to the intro/landing page.
6. Add a new section to the intro page discussing cluster-wide PCAP retention and extraction. This section should include screenshots of:
   • The PCAP filter dialog box
   • The cloud storage configuration/view

Why Is This Needed?

PCAP Snapshots is a key differentiator — the ability to get retrospective cluster-wide packet captures filtered by BPF, node, and time in a single click is a powerful capability that deserves prominent, clear documentation. The current "Traffic Snapshots" naming undersells the feature, and the existing docs lack sufficient detail and visual aids.

Additional Context

• Sub-issue: Add PCAP Snapshots description to README.md kubeshark#1870 (Add PCAP Snapshots description to README.md)

UI/UX Expectations (optional)

Screenshots to capture and include:

• PCAP filter dialog — for the Snapshots page and the new intro section
• Cloud storage view — for the new PCAP retention/extraction intro section