refactor: strengthen architecture CI gates and runtime contracts

pyproject.toml

@@ -110,6 +110,7 @@ dev = [
     "pytest-asyncio~=1.4.0",
     "pytest-cov~=7.1.0",
     "pytest-timeout~=2.4.0",
+    "ruff~=0.16.4",
 ]
 runtime-standard = [
     "Brotli==1.2.0",
@@ -125,6 +126,14 @@ runtime-free-threaded = [
     "psycopg[c]==3.3.4",
 ]
 
+[tool.ruff]
+target-version = "py314"
+line-length = 120
+exclude = ["app/plugins"]
+
+[tool.ruff.lint]
+select = ["E4", "E7", "E9", "F", "I"]
+
 [tool.uv]
 package = false
 required-version = "==0.12.5"