PriceRouter is now multi-vendor and agent-callable

PriceRouter exposes every dynamic-pricing vendor we host behind one API. The capability descriptor lists providers and models so AI agents can pick the right one without hand-coded routing.

PriceRouter is "OpenRouter for price computation": one OpenAPI surface in front of multiple pricing vendors. The capability endpoint now returns the list of providers, their descriptions, and the models we expose for each, so an agent can call `GET /api/price-router` and discover what is available without scraping docs.

New `GET /api/price-router` capability endpoint

`PriceRouterCapability` OpenAPI schema with `providers[]` (id, display name, description, model count) and per-builtin `provider`

Built-ins named `lastprice/<provider>-<model>` so the provider is unambiguous from the function name alone

Dashboard reframes PriceRouter as multi-vendor: clickable catalog, compare-strategies view, explain-after-run, and a downloadable tool manifest for agent frameworks

Snippets switched to safe JSON-to-Python literal conversion so copy-pasted examples run on first try

POST body now uses proper context nesting and returns the actual response shape (previous docs had drift)