fix(uninstall): clean both PowerShell profiles and stop tests polluting real profiles

[mose-zm]

Summary

Fixes post-uninstall PowerShell startup errors (Import-Module ... nvm.psm1 not found) and the root cause behind them.

Bug 1 — uninstall only cleaned ONE PowerShell profile:
install/repair code historically wrote to both the PowerShell 7 (Documents\PowerShell) and Windows PowerShell 5.1 (Documents\WindowsPowerShell) profiles, but remove_from_shell_config only cleaned the one detect_shell_config prefers. The other kept a stale Import-Module, erroring on every shell start after uninstall.

• Windows: clean both candidate profiles on uninstall/deinit.
• Strip rules strengthened: nvm.psm1/nvm.sh integration lines are now always removed — including legacy literal-temp-path variants written by old versions (these could not be matched by nvm_dir and accumulated by the hundreds on a real user machine).

Bug 2 — tests polluted real user profiles:
The temp-dir write guard only checked TMPDIR, which never exists on Windows, so un-isolated tests wrote hundreds of literal .tmp* PATH lines into real profiles.

• New shared guard nvm_dir_in_temp checks TMPDIR/TMP/TEMP; applied to update_shell_config, migrate_rc_to_shim_mode, and init ensure_shell_config.
• Closed isolation gaps: ps_repair test no longer scans real profiles; install_integrity, use_uninstall, and common::run_isolated_with_home now isolate USERPROFILE too.

Test plan

• cargo fmt --check, cargo clippy --all-targets -- -D warnings, cargo test --all (local, all green)
• New Windows regression test: uninstall --self cleans both profiles, preserves user content
• New unit tests: legacy literal-line stripping, temp-guard detection (positive + negative)
• L3 deep security review: 0 findings
• CI green on Ubuntu / Windows / macOS