fix(shell-native): enable winit Linux backends + LF line endings for cross-OS CI

Two unrelated CI failures on the P0 probe gate matrix, fixed together
because both gate the same workflow:

1. ubuntu-latest: winit 0.30 with `default-features = false` triggers
   `compile_error!("The platform you're compiling for is not supported by
   winit")` because no Linux backend (`x11` / `wayland`) is enabled.
   Adds explicit `["x11", "wayland", "wayland-csd-adwaita", "rwh_06"]`
   features so the prod skeleton dep compiles on every desktop OS.
   macOS / Windows backends auto-activate via `cfg(target_os)`, so they
   don't need explicit features.

2. windows-latest: `cargo fmt --check` failed with `Incorrect newline
   style` — actions/checkout normalized .rs files to CRLF on the
   Windows runner, but rustfmt.toml pins `newline_style = "Unix"`.
   Adds `.gitattributes` enforcing `eol=lf` on all text (and explicit
   `*.rs` / `*.toml`) so checkouts stay LF on every platform.

Both fixes are minimal and scoped to the P0 probe gate. The transient
dev-dep block (skia-safe / glutin / glow / etc.) is unchanged.

.gitattributes

@@ -0,0 +1,22 @@
+# Force LF on all text files when checking out (so cross-OS rustfmt
+# `newline_style = "Unix"` stays green on Windows runners). Without this
+# Windows checkout normalizes to CRLF, breaking `cargo fmt --all -- --check`.
+* text=auto eol=lf
+
+# Rust sources must remain LF — explicit override.
+*.rs text eol=lf
+*.toml text eol=lf
+
+# Binary files Git should not touch.
+*.png binary
+*.jpg binary
+*.jpeg binary
+*.gif binary
+*.webp binary
+*.ico binary
+*.icns binary
+*.pdf binary
+*.zip binary
+*.gz binary
+*.tar binary
+*.bin binary

crates/openpencil-shell-native/Cargo.toml

@@ -22,8 +22,15 @@ openpencil-shell-core = { path = "../openpencil-shell-core", version = "0.1.0" }
 # 原因：Rust 1.80 toolchain (rust-toolchain.toml) 对 home/hashbrown 等 crate 当前
 # 版本的 edition2024 / MSRV 1.81+ 需求不兼容，加完整依赖会导致下载阶段失败。
 # 详见提交说明 + Phase 1 Gate codex review。
+#
+# winit features 说明：on Linux 必须显式开 `x11` 和/或 `wayland`，否则
+# `platform_impl/mod.rs` 触发 `compile_error!("The platform you're compiling for is
+# not supported by winit")`. macOS / Windows 各自的 backend 通过 cfg(target_os)
+# 默认启用，不需要 feature flag。Step 1a 只在三大桌面 OS 跑 CI，所以同时打开
+# x11 + wayland 两个 Linux backend 就够。Stage F 真正接 RenderBackend 时会
+# 重新审视（可能加 `serde` / `rwh_06` 等）。
 [target.'cfg(not(target_arch = "wasm32"))'.dependencies]
-winit = { version = "0.30", default-features = false }
+winit = { version = "0.30", default-features = false, features = ["x11", "wayland", "wayland-csd-adwaita", "rwh_06"] }
 
 # TRANSIENT (Step 1a P0 CI gate only — reverted after notes commit, before Task 1 starts).
 # These deps power `examples/p0_probe.rs` + `tests/p0_probe.rs` (gated `#[ignore = "P0_PROBE_GATE"]`).