fix(platform): read proc version with utf-8

[Ghraven]

Summary

is_wsl() now reads /proc/version with explicit UTF-8 decoding and errors="ignore", matching the defensive proc/system-file reads already used elsewhere in the platform compatibility helpers. The existing WSL detection regression test now asserts that the tolerant read options are used.

Target branch

• This PR targets dev, not main. All PRs land in dev; main is curated by the maintainer at each release. If your PR is on main by accident, click "Edit" on this PR and change the base.

Linked Issue

Closes #3902

Type of Change

• Bug fix (non-breaking — fixes a confirmed issue)
• New feature (non-breaking — adds new behaviour)
• Breaking change (changes or removes existing behaviour)
• Refactor / cleanup (behaviour unchanged)
• Documentation only
• CI / tooling / configuration

Checklist

• I searched open issues and open PRs — this is not a duplicate.
• This PR targets dev
• My changes are limited to the scope described above — no unrelated refactors or whitespace changes mixed in.
• I actually ran the app (docker compose up or uvicorn app:app) and verified the change works end-to-end. Type-checks and unit tests are not enough.

How to Test

1. Run the focused WSL detection tests:

   .\\venv\\Scripts\\python.exe -m pytest tests/test_platform_compat.py::test_is_wsl_true_when_proc_version_mentions_microsoft tests/test_platform_compat.py::test_is_wsl_false_when_proc_version_is_not_microsoft tests/test_platform_compat.py::test_is_wsl_false_on_non_posix_without_proc_probe

2. Confirm the tests pass; locally this returned 3 passed.
3. Optionally run the full platform compatibility file. On my Windows checkout, that currently exposes an unrelated pre-existing failure in test_get_wsl_windows_user_profile_falls_back_to_users_dir.

Visual / UI changes — REQUIRED if you touched anything that renders

This PR does not touch UI, rendering, CSS, HTML, SVG, or static/js/ code.

Screenshots / clips

Not applicable; no visual changes.

[alteixeira20]

LGFM. This is a tiny platform-compatibility fix: /proc/version is now read with explicit UTF-8 decoding and ignored decode errors, which is appropriate for WSL detection.

The regression test verifies the new open options, current CI is green, and the change is limited to the intended platform-detection path.