feat(gui): add FastAPI + Jinja2 + HTMX scaffold

- FastAPI app with Jinja2 templates and Pico CSS + HTMX from CDN
- Routes: GET / (placeholder page), GET /health (JSON healthcheck)
- systemd unit (no Install section - manual start only)
- TestClient tests for both endpoints

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

pyproject.toml

@@ -15,11 +15,15 @@ dependencies = [
     "asyncpg>=0.31.0",
     "cloudevents>=2.0.0",
     "cryptography>=44.0.0",
+    "fastapi>=0.115.0",
+    "jinja2>=3.1.6",
     "nats-py>=2.14.0",
     "pydantic>=2,<3",
     "pydantic-settings>=2.7.0",
+    "python-multipart>=0.0.20",
     "shapely>=2.0",
     "tenacity>=9.1.4",
+    "uvicorn[standard]>=0.34.0",
 ]
 
 [project.scripts]
@@ -27,12 +31,14 @@ central-supervisor = "central.supervisor:main"
 central-archive = "central.archive:main"
 central-migrate = "central.migrate:main"
 central-cli = "central.cli:main"
+central-gui = "central.gui:main"
 
 [tool.hatch.build.targets.wheel]
 packages = ["src/central"]
 
 [dependency-groups]
 dev = [
+    "httpx>=0.28.0",
     "mypy>=2.1.0",
     "pytest>=9.0.3",
     "pytest-asyncio>=1.3.0",