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/routers/__init__.py

@@ -0,0 +1,3 @@
+from fin_hub.routers.runway import create_runway_router
+
+__all__ = ["create_runway_router"]

src/fin_hub/routers/runway.py

@@ -0,0 +1,100 @@
+"""Runway read router factory (hub-core pattern)."""
+
+from __future__ import annotations
+
+import os
+from collections.abc import Callable
+from pathlib import Path
+
+from fastapi import APIRouter, HTTPException, Query
+
+from fin_hub.schemas.runway import MonthlyBurnRead, RunwayAlertRead, RunwayProjectionRead, RunwaySummaryRead
+from fin_hub.services.evaluate import evaluate_runway
+from fin_hub.services.ledger import default_ledger_path, get_opening_balance, monthly_summary
+LedgerPathResolver = Callable[[str | None], Path]
+
+
+def _default_ledger_path_resolver(ledger: str | None) -> Path:
+    if ledger:
+        return Path(ledger)
+    env_path = os.environ.get("FIN_HUB_LEDGER")
+    if env_path:
+        return Path(env_path)
+    return default_ledger_path()
+
+
+def _projection_from_dict(runway: dict) -> RunwayProjectionRead:
+    months = runway["months_remaining"]
+    if months == float("inf"):
+        months_remaining: float | None = None
+        label = "unlimited"
+    else:
+        months_remaining = float(months)
+        label = f"{months_remaining:.1f}"
+    return RunwayProjectionRead(
+        current_balance=float(runway["current_balance"]),
+        monthly_burn=float(runway["monthly_burn"]),
+        months_remaining=months_remaining,
+        months_remaining_label=label,
+        alert_threshold_months=float(runway["alert_threshold_months"]),
+        below_threshold=bool(runway["below_threshold"]),
+        currency=str(runway["currency"]),
+        computed_at=str(runway["computed_at"]),
+    )
+
+
+def create_runway_router(
+    *,
+    prefix: str = "/runway",
+    ledger_path_resolver: LedgerPathResolver | None = None,
+) -> APIRouter:
+    resolve_ledger = ledger_path_resolver or _default_ledger_path_resolver
+    router = APIRouter(prefix=prefix, tags=["runway"])
+
+    @router.get("/monthly-burn", response_model=list[MonthlyBurnRead])
+    def get_monthly_burn(
+        ledger: str | None = Query(default=None, description="Ledger database path override"),
+        currency: str | None = Query(default=None, description="Filter rollups by currency"),
+    ) -> list[MonthlyBurnRead]:
+        ledger_path = resolve_ledger(ledger)
+        if not ledger_path.exists():
+            raise HTTPException(status_code=404, detail=f"Ledger not found: {ledger_path}")
+        rollups = monthly_summary(ledger_path=ledger_path)
+        if currency:
+            rollups = [rollup for rollup in rollups if rollup.currency == currency.upper()]
+        return [MonthlyBurnRead(**rollup.as_dict()) for rollup in rollups]
+
+    @router.get("/summary", response_model=RunwaySummaryRead)
+    def get_runway_summary(
+        ledger: str | None = Query(default=None, description="Ledger database path override"),
+        balance: float | None = Query(default=None, description="Override stored opening balance"),
+        threshold: float = Query(default=3.0, ge=0.0),
+        currency: str = Query(default="EUR", min_length=3, max_length=3),
+        allocated: float | None = Query(default=None, ge=0.0),
+        spent: float | None = Query(default=None, ge=0.0),
+    ) -> RunwaySummaryRead:
+        ledger_path = resolve_ledger(ledger)
+        if not ledger_path.exists():
+            raise HTTPException(status_code=404, detail=f"Ledger not found: {ledger_path}")
+        try:
+            report = evaluate_runway(
+                ledger_path=ledger_path,
+                opening_balance=balance,
+                alert_threshold_months=threshold,
+                currency=currency.upper(),
+                allocated=allocated,
+                spent=spent,
+            )
+        except ValueError as exc:
+            raise HTTPException(status_code=422, detail=str(exc)) from exc
+
+        stored_balance, stored_currency = get_opening_balance(ledger_path)
+        return RunwaySummaryRead(
+            runway=_projection_from_dict(report["runway"]),
+            alerts=[RunwayAlertRead(**alert) for alert in report["alerts"]],
+            opening_balance=balance if balance is not None else stored_balance,
+            opening_balance_currency=currency.upper() if balance is not None else stored_currency,
+            ledger_path=str(ledger_path.resolve()),
+        )
+
+    return router