Window: remember the window's size and position between launches

[pravdomil]

Problem

The app window opened at a fixed 1680 × 1020, wherever the system put it, on every launch. Nothing saved its geometry.

Fix

• New apps/effectcraft/src/window.rs (ported from VectorCraft's window module, same conventions): the window's size, position and maximized state are saved to window.json in the config directory, when they change (at most once a second, so a session that ends badly still has them) and on exit.
• The next launch restores them, moved onto a monitor that is still connected; a window bigger than its screen opens maximized.
• The first launch fits the window to its screen (maximized where the default size leaves no room for a Dock or taskbar).
• A window restored maximized keeps the size it returns to (its first frames report the maximized size as an ordinary one).
• Agent-driven runs (--control) restore the saved window but don't overwrite it.
• A damaged or oversized window.json is ignored.
• winit (already in the build through eframe) becomes a dependency on every platform, not just macOS; serde is added to the app crate.

Testing

• 6 new unit tests in window.rs (placement, monitor changes, damaged values, tracking, save/load round trip, maximized restore): pass.
• Manually on macOS with a scratch EFFECTCRAFT_CONFIG_DIR: a seeded geometry (normal and maximized) is restored and tracked back unchanged; a first launch writes the fitted geometry.
• cargo fmt --check and cargo clippy --workspace --all-targets --release -- -D warnings pass. The rest of cargo xtask ci (full workspace tests, layers, assets, wasm) was not run to completion locally.
• Not tested on Windows or Linux.

🤖 Generated with Claude Code