feat(infra): design-reviewer agent + PR helper (US-24 + US-25)

US-24 — Process hygiene UI:
- New .claude/agents/design-reviewer.md (model: opus, read-only) — visual + design-system reviewer that runs after frontend-builder and before code-reviewer. Audits alignment, DESIGN.md tokens, light/dark consistency, typo hierarchy, whitespace rhythm, responsive sanity at 1280x720, button convention, V1 a11y. Output format mirrors code-reviewer.
- Updated .claude/agents/frontend-builder.md DoD: screenshots are MANDATORY (one per feature/state introduced or modified, light+dark when theming is in scope). Hard block on "Dev server not started" — must be flagged explicitly. Screenshots feed the design-reviewer step.

US-25 — PR helper:
- scripts/open-pr.sh wraps `POST /api/v1/repos/{owner}/{repo}/pulls`. Detects host/owner/repo from `git remote get-url origin`, reads basic-auth credentials from `~/.git-credentials` (same source as `git push`, no token in env), uses jq to compose the multiline-safe payload. Validates args, prints PR URL on success, exits non-zero with the server message on failure.
- Makefile target `open-pr TITLE="..." BODY=path/to/body.md [BASE=main]` wraps the script with the same arg validation.
- README.md "Make targets" table extended.

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

Makefile

@@ -7,7 +7,7 @@ VOLUME ?= mimic-data
 # Override explicitly with `make <target> CONTAINER_CMD=podman` or `export CONTAINER_CMD=podman`.
 CONTAINER_CMD ?= $(shell if command -v docker >/dev/null 2>&1; then echo docker; else echo podman; fi)
 
-.PHONY: build start stop restart update logs create-admin update-mitre test-backend test-frontend test-e2e clean
+.PHONY: build start stop restart update logs create-admin update-mitre test-backend test-frontend test-e2e clean open-pr
 
 build:
 	$(CONTAINER_CMD) build -f docker/Dockerfile -t $(IMAGE) .
@@ -60,3 +60,15 @@ clean:
 	-$(CONTAINER_CMD) rm -f $(CONTAINER) 2>/dev/null
 	-$(CONTAINER_CMD) volume rm $(VOLUME) 2>/dev/null
 	rm -rf backend/__pycache__ frontend/node_modules frontend/dist
+
+# Open a PR on the Gitea repo for the current branch.
+#   make open-pr TITLE="feat: sprint 4 — ..." BODY=path/to/body.md [BASE=main]
+# Uses scripts/open-pr.sh, which reads ~/.git-credentials (no token in env).
+open-pr:
+ifndef TITLE
+	$(error TITLE is required: make open-pr TITLE="feat: ..." BODY=path/to/body.md)
+endif
+ifndef BODY
+	$(error BODY is required: make open-pr TITLE="feat: ..." BODY=path/to/body.md)
+endif
+	./scripts/open-pr.sh --title "$(TITLE)" --body "$(BODY)" --base "$(if $(BASE),$(BASE),main)"