kennethfan/dsh-sandbox-tune

Lets build commands run inside the DSH sandbox instead of asking for elevation on every invocation: redirects pure caches (GOCACHE, NPM_CONFIG_CACHE, BUN_INSTALL_CACHE_DIR, PIP_CACHE_DIR) to a temp root, or grants the real cache directories write access in place so they stay shared with the terminal. Dependency stores (GOMODCACHE, CARGO_HOME) are never redirected, only granted. Adds optional user-directory grants (~/.config and friends, all off by default) and a command allowlist that matches exact strings or per-segment after splitting on &&, ||, ; and |, while rejecting redirects that write files (fd duplication like 2>&1 and /dev/null are allowed), command substitution and backgrounding outright. Settings are per-profile or per-session; file edits apply without a restart.