Implement FIN-WP-0001-T06 HTTP runway read surface

Add create_runway_router() following the hub-core factory pattern,
expose GET /runway/summary and /runway/monthly-burn via create_app,
and add finhub serve for local operation.

src/fin_hub/app.py

@@ -0,0 +1,33 @@
+"""Fin-hub FastAPI application factory."""
+
+from __future__ import annotations
+
+from fastapi import FastAPI
+from pydantic import BaseModel
+
+from fin_hub import __version__
+from fin_hub.routers import create_runway_router
+
+
+class HealthResponse(BaseModel):
+    service: str
+    status: str
+    version: str
+
+
+def create_app() -> FastAPI:
+    app = FastAPI(
+        title="Fin Hub API",
+        version=__version__,
+        description="Read surfaces for runway projection and monthly burn.",
+    )
+
+    @app.get("/healthz", response_model=HealthResponse, tags=["system"])
+    def healthz() -> HealthResponse:
+        return HealthResponse(service="fin-hub", status="ok", version=__version__)
+
+    app.include_router(create_runway_router())
+    return app
+
+
+app = create_app()