fix(agent): resolve ModuleNotFoundError for backend, add E2E test infra

- Dockerfile.agent: fix CMD (python -m src.agent.run), use backend/requirements.txt,
  minimal COPY (only src.agent + src.core.cot_logger), add GRACE contract
- docker-compose.yml: SERVICE_TOKEN_SECRET -> SERVICE_JWT (match code)
- docker-compose.enterprise-clean.yml: same env var fix
- docker/.env.agent.example: same env var fix
- build.sh: same env var fix
- chore: semantics-testing SKILL.md, backend tests, pyproject.toml

frontend/vitest.coverage.tmp.config.js

@@ -0,0 +1,17 @@
+import { defineConfig } from 'vitest/config';
+import { svelte } from '@sveltejs/vite-plugin-svelte';
+
+export default defineConfig({
+  plugins: [svelte()],
+  test: {
+    globals: true,
+    environment: 'jsdom',
+    coverage: {
+      provider: 'istanbul',
+      reporter: ['text', 'lcovonly'],
+      clean: false,
+      include: ['src/lib/**/*.{js,ts,svelte}'],
+      exclude: ['**/__tests__/**', '**/*.test.*', '**/*.spec.*', '**/locales/**', '**/mocks/**'],
+    },
+  },
+});