#3255 [Other] Terminal tests: pass on Linux desktops and in a checkout with run configs

Descripción

## Problem and result
`python -m pytest tests/terminal` had five failures on Ubuntu caused by the tests, not by the code. After this PR they pass on Linux. The Windows assertions are unchanged.

- **discovery** (2): the tests wrote the command-line settings file to `%APPDATA%/Strata/settings.json`. Linux reads `$XDG_CONFIG_HOME/strata/settings.json`. A third test passed on Linux only because it wrote to that unread file. All three now use `discovery.own_settings_file()`.
- **discovery** (1): `Catalog` looks "here" in the folder it runs from, this checkout. A developer checkout that holds its own `strata-*.json` (an install from source) beat the mocked app install. The test points "here" at its temporary folder.
- **docker**: `docker/smoke-test.sh` starts `#!/bin/bash` and uses process substitution; it was parsed with `sh`, which is dash on Debian/Ubuntu (`Syntax error: redirection unexpected`). Scripts with a bash shebang are now parsed with bash; the image's sh scripts are still parsed with sh.
- **launch TUI**: since d2a38c9e the Linux cloudflared hint is long enough that "quick tunnel" wraps onto two rows. Whitespace is collapsed before the check.
- **private files**: on POSIX `is_unshared()` is documented as the same check as `is_private()`, so a fresh file under a normal 0002/0022 umask is not unshared. The POSIX branch now asserts the two agree.

## Related discussion
none. Test-only change.

## Approach
Test files only: `tests/terminal/test_discovery.py`, `test_docker_files.py`, `test_launch_tui.py`, `test_private_files.py`. No product code.

## Validation
**Passed:**
- Ubuntu, Python 3.12.3, venv with `requirements.txt` and `requirements-monitor.txt`: the four files give 98 passed, 9 skipped.
- Full `python -m pytest tests/terminal -q`, this branch with the procs fix (#3254) merged, in a checkout with a `strata-*.json` at the root: 852 passed, 17 skipped, 0 failed.
- Same-day clean `main` e88ee39d baseline: 6 failed (the five here plus the procs one), 846 passed, 17 skipped.

**Failed:**
none observed.

**Not run:**
- Windows and macOS: not available. The Windows-only assertions were left as they were.

## Limits
Note for anyone running the suite: a venv without `requirements.txt` makes the 7 lifecycle tests and the runtime test fail with "the server exited with 5 before it was ready" (missing `requests`, Pillow). That is not changed here.

🤖 Generated with [Claude Code](https://claude.com/claude-code)