Release 2.0.0 — explicit monorepo_url, drop first-target-host inference

Breaking change. The monorepo's gitea host was previously inferred from the
first target's subrepo_url, silently coupling the two and breaking on any
multi-host setup (monorepo on host A, target on host B). v2.0.0 replaces the
inference with a required josh.monorepo_url field that mirrors subrepo_url —
same parsing, same SSH/HTTPS auth options, same shape.

- schema_version: 2 is now required; v1 configs are rejected with a clear migration error
- josh.monorepo_url is required; josh.monorepo_auth is optional (default https)
- mono_auth_url() in lib/auth.sh mirrors subrepo_auth_url()
- MONOREPO_API derives from monorepo_url's host instead of .[0].gitea_host;
  env-var override preserved as escape hatch
- initial_import() and force-push call mono_auth_url() instead of building URLs inline
- ADR-012 documents the rationale; CHANGELOG includes migration snippet

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/sync.sh

@@ -475,12 +475,7 @@ initial_import() {
   log "INFO" "=== Initial import: subrepo/${subrepo_branch} → mono/${mono_branch}:${subfolder}/ ==="
 
   # 1. Clone monorepo (directly, not through josh — we need the real repo)
-  local mono_auth_url
-  local api_host_path
-  api_host_path=$(echo "$MONOREPO_API" | sed 's|https://||; s|/api/v1/repos/|/|')
-  mono_auth_url="https://${BOT_USER}:${GITEA_TOKEN}@${api_host_path}.git"
-
-  git clone "$mono_auth_url" \
+  git clone "$(mono_auth_url)" \
     --branch "$mono_branch" --single-branch \
     "${work_dir}/monorepo" || die "Failed to clone monorepo"