Required path param not enforced on bare no-body invocations

## Bug

A required path param is not enforced when a by-id operation is invoked with no flags: bare `growthbook features get` builds `GET /api/v2/features/` with an empty id and returns rc 0 instead of erroring. Providing any other flag restores enforcement (`features get --with-revisions all` → `missing required flag: --id`).

## Root cause (Speakeasy-generated code)

`internal/flagutil/metadata.go` `BuildRequest()` has a body-relaxation heuristic: when `bodyFieldPath == ""` and no flags changed, it calls `relaxRequiredForBodyFields` which sets **all** fields `Required=false` (so a fully-optional body can run argless). GET/DELETE-by-id ops also pass `bodyFieldPath == ""` (they have no body), so the path param's required check is wrongly relaxed on a zero-flag invocation.

Verified against the real call distribution: no-body ops pass `("","")`, whole-struct-body ops pass `("","body")`, sub-field-body ops pass `("Body","body")` — so `bodyFlagName` cleanly separates real-body from no-body ops.

## Stopgap fix (retire when upstream is fixed)

Lives in `.speakeasy/patches/internal/flagutil/metadata.go.patch`: gates the relaxation on `bodyFlagName != ""`, so it only relaxes ops that actually take a body. No-body GET/DELETE-by-id ops now enforce their path param; all-optional list/body ops still run argless.

**To retire:** once Speakeasy scopes the relaxation to actual body operations, remove `metadata.go.patch` and regenerate.

## Refs

- Introduced by #14
- Upstream generator bug — should also be filed to speakeasy-api/speakeasy.

Start with internal/flagutil/metadata.go and .speakeasy/patches/internal/flagutil/metadata.go.patch, then trace BuildRequest's body-relaxation heuristic. Reproduce with `growthbook features get` and `growthbook features get --with-revisions all`; done means the bare by-id invocation rejects the missing path parameter while fully optional body or list operations remain usable without flags.

Written by the indexing model from the issue text.