ops: document deploy secrets and enforce main branch protection

docs/BRANCH_PROTECTION.md

@@ -0,0 +1,35 @@
+# Branch Protection (Codeberg)
+
+`main` should be protected to satisfy constitutional governance (`all changes merge through pull requests`) and to require CI before merge.
+
+## Required settings
+
+- Protected branch: `main`
+- Direct pushes disabled
+- Required approvals: `1` (or stricter)
+- Required status checks:
+  - `ci-gates / checks`
+- Require signed commits: enabled
+
+## Apply via script
+
+```sh
+./scripts/fj-enforce-branch-protection.sh
+```
+
+Optional overrides:
+
+```sh
+EVERY_CHANNEL_FORGE_REPO=every-channel/every.channel \
+EVERY_CHANNEL_PROTECTED_BRANCH=main \
+EVERY_CHANNEL_REQUIRED_CHECKS="ci-gates / checks" \
+EVERY_CHANNEL_REQUIRED_APPROVALS=1 \
+./scripts/fj-enforce-branch-protection.sh
+```
+
+Token source order:
+
+1. `CODEBERG_TOKEN` env var
+2. `secrets/codeberg-token.age` via `agenix` or `age`
+
+The token must have repository admin scope to edit branch protection.