docs: add route-specific priming profiles

[dapi]

Summary

• add an external explanation and glossary entry for context priming;
• introduce the governed Task Context Priming contract with P0 route classification and P1 profiles for every route;
• connect routing and flow entry gates to the matching profile while preserving Feature Flow's immutable-revision GRND-* execution grounding.

Why

Each route needs different evidence before its first lifecycle gate. The change keeps route selection and context collection separate, uses progressive disclosure, and keeps priming results in existing canonical owners instead of creating a duplicate report.

Closes #83.

Validation

• git diff --check
• memory-bank-cli lint --scope-root template/memory-bank --entrypoint template/memory-bank/README.md
• memory-bank-cli doctor --profile template

[dapi]

Superseded by #86, which now targets main and includes this branch.