docs: rewrite README to clarify motivation and zero-trust workflow

[noexecstack]

Summary

• Rewrote README to explain the Cilium OSS 5-minute ring buffer limitation and why this tool exists
• Highlighted the Loki backend as the primary value over Cisco/Isovalent enterprise Timescape
• Added zero-trust workflow: start with default-deny, filter on audit verdicts, generate policies for the gaps
• Promoted Loki as the recommended flow source in Quick Start
• Bumped version to 0.7.6

Test plan

• Review rendered README on the PR for clarity and formatting
• Verify CHANGELOG entry is correct