Repeat held key bindings at the system typematic rate

Holding a paddle bound to a letter produced exactly one character. The
emission loop only acts on edges, so a held paddle sent one key-down and
nothing further until release.

That was the correct consequence of the design rather than a fault in the
send path: auto-repeat is not something Windows synthesises for a key it
believes is down. A physical keyboard repeats because its own firmware
keeps sending make codes while the key is held, and Windows forwards each
one. Injected input has no firmware behind it, so the repeat has to be
generated here.

Re-send the press while the paddle is held, after the user's configured
delay and at their configured rate — SPI_GETKEYBOARDDELAY and
SPI_GETKEYBOARDSPEED — so a paddle behaves like the key it is bound to
rather than at a rate invented here. Both are captured at press time, so
the rate cannot shift mid-hold. The read loop already ticks at report
rate, so this is a per-frame elapsed check with no new thread or timer.

Keys only. Mice do not repeat when held, so mouse-button bindings keep
their one-shot behaviour, and gamepad bindings are held state in the pad
report, where a repeat would mean nothing.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/app/KeyInput.cpp

@@ -151,3 +151,21 @@ void SendKeyInput(uint16_t vk, bool down) {
     if (!down)       input.ki.dwFlags |= KEYEVENTF_KEYUP;
     SendInput(1, &input, sizeof(INPUT));
 }
+
+std::chrono::milliseconds KeyRepeatDelay() {
+    // 0-3, meaning roughly 250ms to 1000ms in 250ms steps.
+    DWORD setting = 1;
+    if (!SystemParametersInfoW(SPI_GETKEYBOARDDELAY, 0, &setting, 0) || setting > 3)
+        setting = 1;
+    return std::chrono::milliseconds(250 * (static_cast<int>(setting) + 1));
+}
+
+std::chrono::milliseconds KeyRepeatInterval() {
+    // 0-31, meaning roughly 2.5 to 30 repeats per second. Windows documents only
+    // the endpoints, so interpolate the rate between them.
+    DWORD setting = 31;
+    if (!SystemParametersInfoW(SPI_GETKEYBOARDSPEED, 0, &setting, 0) || setting > 31)
+        setting = 31;
+    const double perSecond = 2.5 + (30.0 - 2.5) * (static_cast<double>(setting) / 31.0);
+    return std::chrono::milliseconds(static_cast<long long>(1000.0 / perSecond + 0.5));
+}