Add Phase 0a black-box integration test suite

81 tests across 11 files plus a 5-module harness (load, pg, streams,
containers, payloads), covering all eleven Phase 0 goals and all 13 named
chaos-flag pathologies. Talks to the system only over HTTP, Postgres, Redis,
and the Docker CLI -- no imports of application code. RED-BASELINE.md records
the suite failing red against the empty repo before any implementation
existed; README.md documents the request-contract fields invented to fill
gaps in the spec, measurement methodology, and known-flaky tests.

This suite is a frozen contract from this point forward per CLAUDE.md.

tests/test_contract_frontend.py

@@ -0,0 +1,52 @@
+"""G11 -- the frontend and its supporting endpoints are served. No browser
+automation: serving and shape only."""
+import re
+
+import pytest
+
+pytestmark = pytest.mark.contract
+
+
+def _extract_asset_path(html, filename):
+    match = re.search(rf'(?:src|href)=["\']([^"\']*{re.escape(filename)})["\']', html)
+    assert match, f"could not find a reference to {filename} in the index page"
+    path = match.group(1)
+    return path if path.startswith("/") else f"/{path}"
+
+
+async def test_index_serves_html_referencing_assets(api):
+    """G11: GET / returns 200, text/html, and references app.js and style.css."""
+    resp = await api.get("/")
+    assert resp.status_code == 200
+    assert "text/html" in resp.headers.get("content-type", "")
+    body = resp.text
+    assert "app.js" in body
+    assert "style.css" in body
+
+
+async def test_app_js_served(api):
+    """G11: app.js returns 200 with a JS content type."""
+    index_html = (await api.get("/")).text
+    resp = await api.get(_extract_asset_path(index_html, "app.js"))
+    assert resp.status_code == 200
+    ctype = resp.headers.get("content-type", "")
+    assert "javascript" in ctype or "ecmascript" in ctype
+
+
+async def test_style_css_served(api):
+    """G11: style.css returns 200 with a CSS content type."""
+    index_html = (await api.get("/")).text
+    resp = await api.get(_extract_asset_path(index_html, "style.css"))
+    assert resp.status_code == 200
+    assert "css" in resp.headers.get("content-type", "")
+
+
+async def test_accounts_list_endpoint(api):
+    """G11: GET /api/accounts returns >= 100 accounts with the expected shape."""
+    resp = await api.get("/api/accounts")
+    assert resp.status_code == 200
+    accounts = resp.json()
+    assert len(accounts) >= 100
+    sample = accounts[0]
+    for field in ("id", "holder_name", "currency", "balance_minor"):
+        assert field in sample, sample