Add WSL2 Claude Code detection and sync support

[tylergraydev]

Summary

• Detects Claude Code installations inside WSL2 distros from the Windows host via wsl.exe
• Each WSL distro appears as a separate toggleable editor (e.g., "Claude Code (WSL: Ubuntu)") in the settings UI
• MCP config sync writes ~/.claude.json inside WSL distros through wsl.exe commands
• Users with both native Windows and WSL Claude Code can independently enable/disable sync to each
• All WSL code is #[cfg(target_os = "windows")] gated — no-ops on other platforms
• Fixes 12 preexisting TypeScript errors across analytics, sessions, skills, and test files

New files

• src-tauri/src/utils/wsl.rs — WSL2 detection, distro listing, file I/O through wsl.exe, UTF-16LE decoding
• src-tauri/src/services/wsl_config.rs — Config writer for WSL distros (same claude.json format)

Modified files

• Backend: settings.rs, config.rs, models.rs, lib.rs, mod.rs files — WSL editor detection, sync, and command registration
• Frontend: SettingsEditorSyncTab.svelte — WSL editors get amber "W" badge with proper display names
• Type fixes: skill.ts, usageStore.svelte.ts, invokeMock.ts, skillLibrary.test.ts, sessions/+page.svelte

Test plan

• All 859 Rust tests pass
• svelte-check reports 0 errors (down from 12)
• Manual test on Windows with WSL2 installed — verify distros appear in editor list
• Manual test toggling WSL editor and syncing MCPs
• Verify no impact on macOS/Linux builds (WSL code is cfg-gated)