[EXT] Extension manifest `domain.prefixes` is undeclared for the built-in imperative views

[flyingrobots]

Problem

The built-in imperative views (milestone, traceability, blockers, coverage, progress, suggestions, onboarding) use hardcoded prefix logic (n.startsWith('task:') etc.) that doesn't appear in any extension manifest.

This means a future extension system has no way to query which extension "owns" the prefixes used by those views. Graph doctor and future tooling that inspects extension coverage will have blind spots.

Work

Add a roadmap-imperative section to the roadmap manifest (or a separate doc) that catalogs the imperative view prefix dependencies — even if they can't be expressed declaratively yet. Or add an imperativeViews array to the manifest schema for documentation purposes.

Long term: H1 work on extracting built-ins into the Extension system.

Ref: #229 (M11 BLP) / Vision H1

[flyingrobots]

Resolved in 89bb52d (PR #270)