feat: add Windows CreateProcess cmdline budget and prompt fitting

Introduce win-cmdline-limit with pessimistic length estimation (libuv-style
doubling for quoted argv) and tail-preserving prompt truncation when over
budget. Load CURSOR_BRIDGE_WIN_CMDLINE_MAX (clamped 4096–32700, default 30000)
into LoadedEnv and BridgeConfig.

Made-with: Cursor