fix(hooks): keep a hook's broken pipe from crashing the run

[brianjfox]

Summary

• Awaits the write of a lifecycle hook's payload to its stdin, inside a try.
• Records a broken pipe — the hook exited without reading its payload — as that hook's outcome, on its exit status, instead of letting the unhandled rejection take the process down at the end of a finished run.
• Adds a test: a shell hook that handles only postTurn is dispatched a postRun summary larger than the pipe buffers; no unhandled rejection, no hook error logged, exit status recorded. Fails on the unfixed runner, passes on the fixed one, ten runs out of ten.

Verification

• bun run typecheck, bun run build, and bun run lint pass
• bun run test does not complete on this machine on origin/main either: Bun 1.3.13 segfaults partway through the suite (panic: Segmentation fault at address 0x5, SIGTRAP) with or without this branch. bun test src/session/hooks.test.ts passes.
• Reproduced the crash on 0.3.24 with an 89-turn corbits exec run whose hook handled only postTurn: the final summary printed, then EPIPE: broken pipe, send as an unhandled rejection, exit 1, run.json left at running.

Fixes #993