docs: refresh README and stop tracking handoff docs

[user1303836]

Summary

• refresh the README to match the current target-centric V2 architecture, seeded networks, CLI/API surface, and operator workflow
• stop tracking docs/ handoff artifacts in version control and ignore the local docs/ directory
• capture audit follow-up in security: local_file export sink allows arbitrary server-side file writes #130, security: callback and webhook validation can still reach private hosts #131, bug: list_targets ignores pagination when filters are applied #132, and maintenance: cargo audit reports unmaintained runtime dependencies #133

Validation

• cargo test --workspace
• cargo audit

Notes

• this PR does not delete the local docs/ directory; it only removes the tracked handoff artifacts from version control
• no Rust source code or database schema behavior changed in this PR