Correct v0.4 documentation for Agent integration

[moneycaringcoder]

Summary

• remove stale development-only wording for features shipped in v0.4.0
• document versioned Herdr agent recognition and native Agents sidebar behavior
• document the private agent-view.json preference and its presentation-only security boundary
• make quickstart and troubleshooting guidance cover recognition, group labeling, filtering, and recovery
• update the stable Hermes adapter contract and contributor test guidance
• refresh the architecture diagram, popup/overlay boundary, persistence model, and screenshot rationale

Important release note

This corrects documentation on main; it does not rewrite the immutable v0.4.0 tag. A v0.4.1 patch release would be needed if these corrections should become the release-pinned documentation target.

Verification

• python3 tools/check_docs.py
• python3 -m unittest discover -s tools -p 'test_check_docs.py' — 18 passed
• python3 tools/check_package.py --allow-dirty — 52 files verified
• python3 tools/check_public_contracts.py --archive target/package/herdr-tether-0.4.0.crate --binary target/release/herdr-tether — 23 examples verified
• git diff --check