docs(agent-graph): add continuous enrichment skill workflow

[forhappy]

Summary

• add an explicit continuous-enrichment mode to the bundled Compass coding-agent skill
• document pinned Base/Overlay revisions, bounded milestone batching, grounding, CRUD ownership, and source-change rebase gates
• add progressive-disclosure reference material plus install-contract assertions
• document the workflow in the Agent Graph concept, enhancement guide, assistant setup, compatibility notes, command reference, and changelog

Verification

• uv run --with pyyaml python /Users/haipingfu/.agents/skills/skill-creator/scripts/quick_validate.py crates/compass-cli/assets/compass-skill
• CARGO_TARGET_DIR=/Volumes/Workspace/crabbuild-target/compass-continuous-enrichment cargo test -p compass-cli --test install_cli --locked
• CARGO_TARGET_DIR=/Volumes/Workspace/crabbuild-target/compass-continuous-enrichment cargo clippy -p compass-cli --test install_cli --locked -- -D warnings
• sh scripts/check_product_boundary.sh
• git diff --cached --check

cargo fmt --all -- --check reports an existing unrelated formatting difference in crates/compass-ocr/src/engine.rs.