feat(05-01): geo math + fixture RoutingSource backend + public API

- geo.ts: haversineM + deriveCumulativeDistanceM (D-07 snapped-progress field)
- fixture-source.ts: backend #1 — ORIGIN_TOLERANCE_M=200 matching law,
  honest-null pending semantics (D-03), defensive pair skip at index build,
  lazy memoized index (LAW 1), static JSON import (LAW 2), zero
  logging/storage/network (LAW 3, D-12)
- index.ts: named-export public surface, subpath-with-extension import law
- loader proven in three environments (bare Node 24, esbuild, Vite-family)

routing/src/index.ts

@@ -0,0 +1,30 @@
+/*
+ * index.ts — the public API surface of @araharah/routing (D-01, D-03, D-07).
+ * ---------------------------------------------------------------------------
+ * Named exports ONLY (no default export). The package has NO exports /
+ * main field (the @araharah/theme + @araharah/search precedent), so
+ * consumers import the EXPLICIT SUBPATH WITH EXTENSION —
+ *   import { createFixtureRoutingSource } from "@araharah/routing/src/index.ts";
+ * (both tsconfigs carry allowImportingTsExtensions + bundler resolution;
+ * esbuild and Vite compile the .ts source; Node 24 type-stripping handles
+ * the corpus runner's relative form). A bare "@araharah/routing" specifier
+ * resolves to NOTHING — never use it.
+ *
+ * The module reads NO environment, NO secrets, and NO network (D-05/D-12):
+ * the whole routing stack is V8-native and dependency-free — fixtures ride
+ * the bundle, requests never leave the caller's frame.
+ */
+
+export type {
+  RoutePoint, RouteRequest, RouteSummary, RouteStep,
+  RouteGeometry, RouteOption, RouteResult, RoutingSource,
+  FixturePair, FixtureRoute,
+} from "./types.ts";
+export { decodePolyline6, encodePolyline6 } from "./polyline.ts";
+export { haversineM, deriveCumulativeDistanceM } from "./geo.ts";
+export {
+  ORIGIN_TOLERANCE_M,
+  createFixtureRoutingSource,
+  getPairOrigin,
+  getPairs,
+} from "./fixture-source.ts";