fix: [nomad-prep] P8 — spot-check lib/mirrors.sh against empty Forgejo target (#796)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/mirror-bootstrap.md

@@ -0,0 +1,59 @@
+# Mirror Bootstrap — Pull-Mirror Cutover Path
+
+How to populate an empty Forgejo repo from an external source using
+`lib/mirrors.sh`'s `mirror_pull_register()`.
+
+## Prerequisites
+
+| Variable | Example | Purpose |
+|---|---|---|
+| `FORGE_URL` | `http://forgejo:3000` | Forgejo instance base URL |
+| `FORGE_API` | `${FORGE_URL}/api/v1` | API base (set by `lib/env.sh`) |
+| `FORGE_TOKEN` | (admin or org-owner token) | Must have `repo:create` scope |
+
+The target org/user must already exist on the Forgejo instance.
+
+## Command
+
+```bash
+source lib/env.sh
+source lib/mirrors.sh
+
+# Register a pull mirror — creates the repo and starts the first sync.
+mirror_pull_register \
+  "https://codeberg.org/johba/disinto.git" \   # source URL
+  "disinto-admin" \                             # target owner
+  "disinto" \                                   # target repo name
+  "8h0m0s"                                      # sync interval (optional, default 8h)
+```
+
+The function calls `POST /api/v1/repos/migrate` with `mirror: true`.
+Forgejo creates the repo and immediately queues the first sync.
+
+## Verifying the sync
+
+```bash
+# Check mirror status via API
+forge_api GET "/repos/disinto-admin/disinto" | jq '.mirror, .mirror_interval'
+
+# Confirm content arrived — should list branches
+forge_api GET "/repos/disinto-admin/disinto/branches" | jq '.[].name'
+```
+
+The first sync typically completes within a few seconds for small-to-medium
+repos.  For large repos, poll the branches endpoint until content appears.
+
+## Cutover scenario (Nomad migration)
+
+At cutover to the Nomad box:
+
+1. Stand up fresh Forgejo on the Nomad cluster (empty instance).
+2. Create the `disinto-admin` org via `disinto init` or API.
+3. Run `mirror_pull_register` pointing at the Codeberg source.
+4. Wait for sync to complete (check branches endpoint).
+5. Once content is confirmed, proceed with `disinto init` against the
+   now-populated repo — all subsequent `mirror_push` calls will push
+   to any additional mirrors configured in `projects/*.toml`.
+
+No manual `git clone` + `git push` step is needed.  The Forgejo pull-mirror
+handles the entire transfer.