New `exclude` config field per target generates .josh-filters/<name>.josh
files with josh :exclude clauses. Josh-proxy applies exclusions at the
transport layer — excluded files never appear in the subrepo.
Preflight checks that generated filter files are committed.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
New commands for safely onboarding existing subrepos into the monorepo
without losing open PRs:
- josh-sync onboard <target>: interactive, resumable 5-step flow
(import → wait for merge → reset to new repo)
- josh-sync migrate-pr <target> [PR#...] [--all]: migrate PRs from
archived repo to new repo via patch application
Also refactors create_pr() to wrap create_pr_number(), eliminating
duplicated curl/jq logic.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
