chore: reorganize test files into domain-specific subdirectories under tests/

Split the monolithic test directory into three tiers (unit, api, e2e) with a path-mirroring directory structure. Added corresponding Makefile targets (test-unit, test-api, test-e2e) and updated all documentation references (CLAUDE.md, README.md, testing-cicd.html, testing-framework.html, testing-make.html) to reflect the new layout and naming conventions.

tests/api/proxy.py

@@ -0,0 +1,30 @@
+# retoor <retoor@molodetz.nl>
+
+import requests
+from tests.conftest import BASE_URL
+
+
+def test_proxy_unknown_slug_returns_404(app_server):
+    r = requests.get(f"{BASE_URL}/p/nonexistent-slug", allow_redirects=False)
+    assert r.status_code == 404
+
+
+def test_proxy_unknown_slug_json(app_server):
+    r = requests.get(
+        f"{BASE_URL}/p/nonexistent-slug",
+        headers={"X-Requested-With": "fetch"},
+        allow_redirects=False,
+    )
+    assert r.status_code == 404
+
+
+def test_proxy_unknown_slug_with_path(app_server):
+    r = requests.get(
+        f"{BASE_URL}/p/nonexistent-slug/some/path", allow_redirects=False
+    )
+    assert r.status_code == 404
+
+
+def test_proxy_post_unknown_slug(app_server):
+    r = requests.post(f"{BASE_URL}/p/nonexistent-slug", allow_redirects=False)
+    assert r.status_code == 404