fix: dual-timeout held keys to fix terminal initial repeat delay

Root cause: terminals wait 300-500ms after initial Press before
sending the first Repeat event. With 60ms timeout, the key was
released during this gap, causing step-pause-accelerate pattern.

Fix: two timeout phases:
- After Press (no Repeat seen yet): 400ms timeout
  Covers terminal's initial repeat delay, key stays held
- After first Repeat: 80ms timeout
  Repeats arrive every ~30ms, 80ms is safe margin
  Quick release detection once repeating starts

Result: smooth continuous movement from first keypress, no gap

src/input.rs

@@ -44,9 +44,11 @@ pub enum HeldKey {
 
 struct HeldState {
     last_seen: Instant,
+    seen_repeat: bool,
 }
 
-const HOLD_TIMEOUT: Duration = Duration::from_millis(60);
+const HOLD_TIMEOUT_PRESS: Duration = Duration::from_millis(400);
+const HOLD_TIMEOUT_REPEAT: Duration = Duration::from_millis(80);
 
 pub struct InputHandler {
     pub paint_brush: MaterialBrush,
@@ -102,8 +104,11 @@ impl InputHandler {
         }
     }
 
-    fn mark_held(&mut self, key: HeldKey) {
-        self.held.insert(key, HeldState { last_seen: Instant::now() });
+    fn mark_held(&mut self, key: HeldKey, is_repeat: bool) {
+        self.held.insert(key, HeldState {
+            last_seen: Instant::now(),
+            seen_repeat: is_repeat,
+        });
     }
 
     fn release(&mut self, key: HeldKey) {
@@ -119,7 +124,10 @@ impl InputHandler {
         self.jump_pressed = false;
         let now = Instant::now();
 
-        self.held.retain(|_, state| now.duration_since(state.last_seen) < HOLD_TIMEOUT);
+        self.held.retain(|_, state| {
+            let timeout = if state.seen_repeat { HOLD_TIMEOUT_REPEAT } else { HOLD_TIMEOUT_PRESS };
+            now.duration_since(state.last_seen) < timeout
+        });
 
         let events: Vec<Event> = match &self.receiver {
             Some(rx) => rx.try_iter().collect(),
@@ -163,8 +171,10 @@ impl InputHandler {
                 }
 
                 if let Some(held_key) = Self::key_to_held(code) {
-                    if is_press || is_repeat {
-                        self.mark_held(held_key);
+                    if is_press {
+                        self.mark_held(held_key, false);
+                    } else if is_repeat {
+                        self.mark_held(held_key, true);
                     } else if is_release {
                         self.release(held_key);
                     }