feat: add devcontainer based setup docs

docs/contribution/fork-workflow.mdx

@@ -0,0 +1,41 @@
+---
+title: Fork Workflow
+description: Keep your Dograh fork connected to upstream.
+---
+
+The contributor bootstrap script configures two remotes:
+
+- `origin`: your fork, where you push
+- `upstream`: `dograh-hq/dograh`, where new commits land
+
+If you cloned `dograh-hq/dograh` directly instead of your fork, run this once inside the devcontainer after it boots:
+
+```bash
+bash scripts/setup_fork.sh
+```
+
+To pull in upstream changes:
+
+```bash
+git fetch upstream
+git checkout main
+git merge upstream/main
+git push origin main
+```
+
+Check your remotes any time with:
+
+```bash
+git remote -v
+```
+
+You should see:
+
+```bash
+origin    https://github.com/<YOUR_HANDLE>/dograh.git (fetch/push)
+upstream  https://github.com/dograh-hq/dograh.git    (fetch/push)
+```
+
+<Note>
+Always push feature branches to **`origin`** (your fork), then open a pull request against `dograh-hq/dograh:main`. Never push directly to `upstream`.
+</Note>