feat(overlay): discover unclaimed mpv key bindings

- Import non-conflicting mpv bindings for the overlay session
- Preserve SubMiner precedence and document discovery behavior

src/main/runtime/mpv-input-bindings.test.ts

@@ -0,0 +1,41 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import { readMpvInputBindings } from './mpv-input-bindings';
+
+test('discovery reads the connected player and preserves configured keys including disabled bindings', async () => {
+  const client = {
+    connected: true,
+    requestProperty: async (name: string) => {
+      assert.equal(name, 'input-bindings');
+      return [{ key: 'r', cmd: 'script-binding replay/run', priority: 1 }];
+    },
+  };
+  assert.deepEqual(
+    await readMpvInputBindings({
+      getMpvClient: () => client,
+      getConfiguredKeybindings: () => [{ key: 'Ctrl+KeyR', command: null }],
+      platform: 'linux',
+    }),
+    { keys: ['r'], blockedKeys: [{ code: 'KeyR', modifiers: ['ctrl'] }] },
+  );
+});
+
+test('discovery safely handles unsupported properties and disconnects during a request', async () => {
+  const client = {
+    connected: true,
+    requestProperty: async (): Promise<unknown> => {
+      throw new Error('property unavailable');
+    },
+  };
+  const deps = {
+    getMpvClient: () => client,
+    getConfiguredKeybindings: () => [],
+    platform: 'linux',
+  } satisfies Parameters<typeof readMpvInputBindings>[0];
+  assert.deepEqual((await readMpvInputBindings(deps)).keys, []);
+  client.requestProperty = async () => {
+    client.connected = false;
+    return [{ key: 'r', cmd: 'seek 5', priority: 1 }];
+  };
+  assert.deepEqual((await readMpvInputBindings(deps)).keys, []);
+});