fix(probe): correct command-default-location flag, owner-only probe umask, robust binary resolution

[rldyourmnd]

Problem

install-cli failed on the pinned 2470.4 release with:

no such option --command-default-locations

Root cause — three independent defects

1. Wrong CLI flag form. The probe and launch flag builder used --command-default-locations (plural), but Junie accepts --command-default-location (singular) for commands (config/mcp/skill/model stay plural). Verified against junie --help on 2470.4.

2. Probe runtime state not private. Junie is a JVM app that writes ~/.junie under the isolated probe HOME. Under an ambient umask that state is not private and require_private_directory rejected it.

3. resolve_junie_binary not robust. When versions/<v>/junie is the launcher script (a regular file), lstat on versions/<v>/junie/bin/junie raises NotADirectoryError, which escaped the candidate loop (it only caught FileNotFoundError).

Fix

1. Use --command-default-location (singular) in the probe and the launch flag builder.
2. Run the probe under an owner-only umask (0o077) via preexec_fn.
3. Catch NotADirectoryError in the candidate loop so the launcher-script candidate is tried.

Verification

install-cli --target <isolated-target> --json
# { "software": { "version": "2470.4", "state": "installed" }, "software_changed": true }

A matching control-plane test (test_junie_cli_runtime_launch.py argv expectation) is updated in a separate commit. Two pre-existing failures on clean `main` (anchor split inode, bootstrap residue under non-sticky temp) are unchanged.