feat: initial FastAPI boilerplate setup

Set up Webber - multi-agent AI development system with:

- Domain-based project structure (src/domains/, src/shared/)
- BaseController pattern with lazy router instantiation
- Pydantic Settings configuration with env file support
- Logger decorator with temporal benchmarking and trace IDs
- UserProvider singleton for request-scoped context
- Custom exception hierarchy
- Health endpoints (/, /health)

Dependencies (CVE checked 2026-01-09):
- FastAPI 0.128.0, Starlette 0.50.0, Uvicorn 0.40.0
- Pydantic 2.12.4, PydanticAI 1.40.0
- All packages at latest safe versions

Placeholder domains for future implementation:
- agents/ (explore, plan, task)
- tools/ (file, shell, search)
- auth/ (tatlock integration)

Port: 8086 (per CONTAINERS.md allocation)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/domains/router.py

@@ -0,0 +1,26 @@
+"""
+Root router - composes all domain routers.
+
+Import and include domain routers here.
+main.py only includes this root_router.
+"""
+from fastapi import APIRouter
+
+from src.domains.health.router import router as health_router
+# from src.domains.auth.router import router as auth_router
+# from src.domains.agents.router import router as agents_router
+# from src.domains.tools.router import router as tools_router
+
+root_router = APIRouter()
+
+# Health (no prefix - root level)
+root_router.include_router(health_router)
+
+# Auth domain
+# root_router.include_router(auth_router, prefix="/auth", tags=["Auth"])
+
+# Agents domain
+# root_router.include_router(agents_router, prefix="/agents", tags=["Agents"])
+
+# Tools domain
+# root_router.include_router(tools_router, prefix="/tools", tags=["Tools"])