adopt core: bound capture buffers to stop OOM on huge output (upstream #3333 + #3579) #104

Upstream PRs: rtk-ai#3333 by @FlorianBruniaux (cap exec_capture, shared by ~16 filters incl. prisma/vitest/playwright/git) and rtk-ai#3579 by @thebigjc (cap raw retention in search) — related small fixes, one adoption batch.

Bug: capture() and the search path use unbounded cmd.output(), while run_streaming caps at RAW_CAP — a huge eslint JSON or a large-tree search OOM-kills the caller. Rank (b): crash/hang class.

Verified on develop (2026-08-17 sweep): src/core/stream.rs:563-590 unbounded; src/cmds/system/search.rs:1548 unbounded.

Note: rtk-ai#3505 also carries an exec_capture cap hunk — resolve overlap at adoption time.