Isolate daemon environments and expose PID-safe tree kill

[zackees]

Summary

• add EnvironmentPolicy::{Auto, Inherit, UserBaseline, Clear} to contained and detached spawn APIs
• make Auto inherit for contained children and build a fresh Windows user baseline for detached daemons
• expose local process_tree::kill_tree(pid, timeout) without requiring the daemon
• identify targets by PID plus creation time and reject stale PPID relationships after PID reuse
• route running-process's own daemon launch paths and RPC kill-tree handler through the new APIs

Safety boundary

Windows does not expose a supported readback API for the original CreateProcess creation flags of an arbitrary process. This change therefore does not infer daemon intent or broadly reap detached-looking processes. It supplies explicit spawn policy plus a PID-instance-safe tree-kill primitive for callers that already have lifecycle ownership.

Validation

• soldr cargo test -p running-process --lib --no-default-features environment -- --test-threads=1
• soldr cargo test -p running-process --test containment_test test_auto -- --test-threads=1
• soldr cargo test -p running-process --test containment_test test_local_kill_tree -- --test-threads=1
• soldr cargo check -p running-process --all-features --lib
• git diff --check

soldr cargo fmt --all -- --check is already red on unchanged origin/main files under the current toolchain; all touched Rust files were formatted individually.

[zackees]

Consumer rollouts: zackees/soldr#1793, FastLED/fbuild#1169, and zackees/zccache#1192.