Harden SteamFlow install/library handling and remove unused legacy projects

[weter11]

Motivation

• Make library scanning robust when a configured steam library path is invalid and provide clearer diagnostics for failing appmanifest parsing.
• Ensure installs target the persistent Steam library location and persist an appmanifest_<appid>.acf so the scanner can discover newly installed games after restart.
• Remove unused legacy OpenSteamClient projects from the solution and keep documentation in sync with the new behavior.

Description

• Reworked library scanning: added scan_installed_app_paths_pathbuf() and scan_library(&Path) to validate the configured steam_library_path (checks for steamapps) and fall back to auto-detection; added a log line with the chosen root.
• Improved ACF parsing: parse_app_manifest_install_path now prints a warning when appid cannot be parsed instead of silently returning None.
• Persist installs into the real library: install_game now resolves steam_library_path from the launcher config, installs to <steam_library_path>/steamapps/common/<game>, ensures directories exist, and writes a basic appmanifest_<appid>.acf on successful install; added helper methods resolve_install_game_name, write_basic_appmanifest, and sanitize_install_dir.
• Adjusted install/manifest fallback logic so install_root_for_app uses steamapps/common/<appid> when no manifest installdir is present.
• Removed OpenSteamClient.DI and OpenSteamClient.Logging entries and directories from the repository/solution.
• Updated docs: SteamFlow/README.md and SteamFlow/ROADMAP.md now document the Depot Browser entry and the persistent install/appmanifest behavior.

Testing

• Ran cargo fmt --manifest-path SteamFlow/Cargo.toml and it completed successfully.
• Ran cargo check --manifest-path SteamFlow/Cargo.toml and the crate type-checked with only warnings (no errors).

---

Codex Task