feat: agent monitor characters, cast panel, WSL fixes, and Sonnet 4.6 (#149)

## Summary

### New Features
- **Claude Sonnet 4.6 support** — added `claude-sonnet-4-6` as a selectable model in the config sidebar
- **Anime girl characters for subagents** — each subagent in the agent monitor is automatically assigned one of six characters (Amari, Keiko, Minori, Reina, Tatsumi, Yumiko) with a unique name, CDN avatar, title, and lore-flavoured description; assignment avoids duplicates when possible
- **"Meet the Team" cast panel** — a new modal accessible from the status bar introduces the full cast: Naomi (Chief hEx-ecutive Officer), Hikari (Chief Operating Officer), and the six subagent girls with their C-suite titles and character bios

### Bug Fixes
- **"Already running" error on invalid working directory** — if a spawned Claude process exits unexpectedly (e.g. because the working directory doesn't exist), `try_wait()` now detects the stale handle and clears it before allowing a restart
- **Working directory pre-validation** — on Windows, the app now runs `wsl -e test -d <dir>` before launching Claude; invalid directories surface a clear error immediately
- **WSL binary detection** — on Windows, `wsl -e bash -lc "which claude"` is used to probe for the Claude binary inside WSL; on Linux/WSLg, `bash -lc "which claude"` is used as a login-shell fallback so GUI apps find the binary even without shell PATH
- **WSL detection fix for production builds** — `detect_wsl()` now short-circuits at compile time on Windows targets, preventing inherited `WSL_DISTRO_NAME` env vars from misrouting native Windows binaries through the Linux code path

✨ This PR was crafted with love by Hikari~ 🌸

Reviewed-on: #149
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

src-tauri/src/stats.rs

@@ -86,8 +86,9 @@ impl ContextWarning {
 /// Get the context window limit (in tokens) for a given model
 fn get_context_window_limit(model: &str) -> u64 {
     match model {
-        // Claude 4.6 family - 200K standard (1M beta available via header)
+        // Claude 4.6 family
         "claude-opus-4-6" => 200_000,
+        "claude-sonnet-4-6" => 1_000_000, // 1M token context window
         // Claude 4.5 family - 200K standard context
         "claude-opus-4-5-20251101"
         | "claude-sonnet-4-5-20250929"
@@ -502,6 +503,7 @@ pub fn calculate_cost(
     let (input_price_per_million, output_price_per_million) = match model {
         // Current generation (Claude 4.6)
         "claude-opus-4-6" => (5.0, 25.0),
+        "claude-sonnet-4-6" => (3.0, 15.0),
 
         // Previous generation (Claude 4.5)
         "claude-opus-4-5-20251101" => (5.0, 25.0),