agent: wayland — evdev hotkey backend, download resume, SHA256 integrity

Add kon-hotkey crate with evdev-based global hotkey capture that works on
Wayland (and X11). Patterns from whisper-overlay: per-device async listeners,
inotify hotplug with udev permission retry, watch channel for live config
updates. Frontend detects Wayland at startup and selects evdev or
tauri-plugin-global-shortcut automatically.

Model downloads now support HTTP Range resume for interrupted downloads and
optional SHA256 integrity verification (incremental, no second pass).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/hotkey/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "kon-hotkey"
+version = "0.1.0"
+edition = "2021"
+description = "Wayland-compatible global hotkey listener for Kon — evdev backend with device hotplug"
+
+[dependencies]
+kon-core = { path = "../core" }
+tokio = { version = "1", features = ["rt", "sync", "macros", "time"] }
+serde = { version = "1", features = ["derive"] }
+log = "0.4"
+
+[target.'cfg(target_os = "linux")'.dependencies]
+evdev = { version = "0.12", features = ["tokio"] }
+notify = { version = "7", default-features = false, features = ["macos_fsevent"] }
+nix = { version = "0.29", features = ["fs"] }