BuildRequest slurps stdin on no-body ops — GETs hang forever under held-open pipes

**Behavior:** every command — including body-less GETs and `--dry-run` — blocks forever when stdin is a held-open pipe or socket. `tail -f /dev/null | growthbook projects list` hangs with zero output; CI runners and agent harnesses that keep the child's stdin open hit this constantly.

**Root cause:** `BuildRequest`'s "Priority 2: stdin" branch calls `io.ReadAll(stdin)` whenever stdin is a non-char-device, without checking whether the operation takes a body at all.

**Carried fix:** `.speakeasy/patches/internal/flagutil/metadata.go.patch` (PR #48) gates the read on `bodyFlagName != ""`. Body-taking ops keep the stdin-as-body feature (a held-open pipe still blocks those — defensible, documented behavior; see also #25).

**Retire when:** Speakeasy's generated `flagutil/metadata.go` skips the stdin read for no-body operations.

Start with .speakeasy/patches/internal/flagutil/metadata.go.patch and the generated internal/flagutil/metadata.go mentioned in the issue. Inspect BuildRequest's stdin handling and compare the carried fix in PR #48. Done means no-body operations, including GETs and --dry-run, no longer read held-open stdin, while body-taking operations retain stdin-as-body behavior.

Written by the indexing model from the issue text.