feat: add overlay state types and IPC constants

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/types/overlay.ts

@@ -0,0 +1,34 @@
+export type OverlayPersistedState = {
+  url: string;
+  opacity: number;
+  alwaysOnTop: boolean;
+  clickThrough: boolean;
+};
+
+export type OverlayState = OverlayPersistedState & {
+  isOpen: boolean;
+  urlError: string | null;
+  hotkeyError: string | null;
+};
+
+export type OverlayActions = {
+  setUrl: (raw: string) => void;
+  setOpacity: (v: number) => void;
+  setAlwaysOnTop: (v: boolean) => void;
+  setClickThrough: (v: boolean) => void;
+  /** Internal: applies a click-through change that originated in Rust.
+   *  Skips the live-wiring effect to avoid ping-pong with the backend. */
+  _setClickThroughFromBackend: (v: boolean) => void;
+  setHotkeyError: (msg: string | null) => void;
+  setIsOpen: (v: boolean) => void;
+  hydrate: (s: OverlayPersistedState) => void;
+};
+
+export type ClickThroughToggledPayload = { clickThrough: boolean };
+export type ClickThroughNoOverlayPayload = Record<string, never>;
+
+export const STORE_FILE = "browserlay.json";
+export const STORE_KEY = "state";
+export const OVERLAY_LABEL = "overlay";
+export const EVT_CLICK_THROUGH_TOGGLED = "click-through-toggled";
+export const EVT_CLICK_THROUGH_NO_OVERLAY = "click-through-no-overlay";