Initialize the coverage backfill in a .NET repo. Use when setting up dotnet-coverage-kit in a new service for the first time, or when the user says 'init coverage', 'set up coverage backfill', or 'scaffold the coverage manifest'. Detects the repo's architecture and projects, sweeps every source file against an objective per-category signal rubric in parallel (user-chosen agent count) to classify them, synthesizes a coverage-manifest.yml and a per-repo unit-testing overlay at the main agent, runs a single cross-project self-critique to catch wrongly-excluded testable code and wrongly-included untestable code (including the same mistake repeated across projects) before human review, installs the runsettings + run script, and scaffolds a PR coverage workflow without clobbering existing CI.