Make Design Doctrine retrieval and maintenance proactive

[brsbl]

Summary

• rank natural task language without requiring every query word to match
• expose an exact-task Design Doctrine agent tool
• infer a bounded rule shortlist for design-oriented thread titles
• reject detached managed-install caches before maintenance leases history
• document the editable-checkout requirement and publish Design Doctrine 0.3.0
• remove stale UI Pattern Atlas references

Verification

• PATH=/Users/brsbl/.nvm/versions/node/v22.22.1/bin:$PATH npm run check --workspace=plugins/design-doctrine
• 21 tests passed
• live bounded scan succeeded against the editable checkout and its test lease was released
• weekly Design Doctrine automation completed a manual run, validated 33 rules, committed ddr_031, and advanced all leased checkpoints

Stack

Depends on #17, which retires UI Patterns and repairs plugin installs.