feat(enterprise): Phase 14 — API Key Management + SSO/SAML 2.0

- ApiKey model (SHA-256 hash, prefix, scopes, expiry) + Alembic migration (b040ent)
- SsoConfig model for SAML 2.0 IdP settings (attribute mapping, auto-provision)
- API key auth integrated into get_current_user (aegis_ prefix detection)
- Routers: /api/v1/api-keys (full CRUD + revoke) and /api/v1/sso (metadata, login, callback, config)
- python3-saml added to requirements; Dockerfile adds libxmlsec1-dev for SAML XML signing
- QA script: 52 assertions covering key lifecycle, API key auth, SSO config

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/Dockerfile

@@ -7,6 +7,10 @@ RUN apt-get update && apt-get install -y \
     gcc \
     libpq-dev \
     curl \
+    pkg-config \
+    libxml2-dev \
+    libxmlsec1-dev \
+    libxmlsec1-openssl \
     && rm -rf /var/lib/apt/lists/*
 
 # Copy requirements first for better caching