Migrate to Runpod REST v2

Moves a codebase off the GraphQL API (api.runpod.io/graphql) and REST v1 (rest.runpod.io/v1) onto REST v2 (api.runpod.io/v2).

The payoff, in one line each — you deliver these to the user at step 6, matched to their actual code. Don't recite them now:

• See stock before you rent — GET /v2/catalog/gpus?include=AVAILABILITY&product=POD. v1 had no catalog at all, so every capacity retry loop was blind.
• Endpoints return their own job URLs — requestUrls.run, no more string-building.
• Real lifecycle states — PROVISIONING/STARTING/ERROR and an actions list, so wait-loops fail fast instead of timing out.
• Mistakes fail loudly — unknown request fields are rejected by name, with structured errors and honest status codes.

The full set, organized as if their code does X → v2 offers Y: reference/unlocks.md — open it at step 6.