docs(shell): state the zoom bridge's return contract precisely

`adjustZoomLevel` steps by `stepZoomLevel`'s rules; a stored out-of-range
level is never moved against the request, so the returned level is not
itself guaranteed to be within `ZOOM_LEVEL_MIN..ZOOM_LEVEL_MAX`.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

CLAUDE.md

@@ -769,7 +769,7 @@ This project uses modern Angular signal-based APIs and patterns. **ALWAYS** use
 - Bootstraps Electron app and initializes database
 - Registers event handlers for IPC communication
 - Creates the main window per the startup window mode (`app/app.ts` `initMainWindow`, resolver in `app/services/startup-window-mode.ts`): the electron-conf `STARTUP_WINDOW_MODE` mirror or the one-shot `--fullscreen` switch (consumed by the first window, so a window the macOS Dock re-creates in the same process follows the stored setting); `fullscreen: true` is a constructor option that Windows/Linux honour before the first paint, while macOS ignores it on a hidden window, so `ready-to-show` repeats the request after `show()` only when `isFullScreen()` is still false, through the same tracker the F11 toggle uses (`app/services/native-fullscreen-transitions.ts`: per-window fullscreen state seeded once at creation via `trackNativeFullScreen` and fed only by the enter/leave events afterwards, plus a pending record holding the latest target, cleared when an event lands on it, kept when an event lands on the other state, and ignored after 2 s; the tracker only observes and never issues a request itself, since a "repeat on mismatch" cannot be told apart from reversing the user's own green-button action — a toggle is never decided against `isFullScreen()`, which is stale mid-transition and, on Windows, even during the event), so F11 during the startup animation exits instead of re-requesting; `maximize()` waits for `ready-to-show` too (it would show a hidden window early). `attachWindowStateEvents` tracks native and HTML-element fullscreen as two flags OR-ed into `WINDOW:STATE_CHANGED`, because Electron leaves only the HTML state when the window was already natively fullscreen
-- Persists the app zoom level (issue #1109): the preload restores it with `webFrame.setZoomLevel` (temporary, frame-bound zoom; level answered over the synchronous `WINDOW:GET_ZOOM_LEVEL` IPC, applied at `DOMContentLoaded` and acknowledged with `WINDOW:ZOOM_LEVEL_APPLIED` — any earlier `webFrame.setZoomLevel` leaves a hidden Linux/Windows window without `ready-to-show`), never `webContents.setZoomLevel` — under `file://` Chromium keys zoom by the full URL, so the app's path routing would reset it on the next resize after a section change, and dev mode (`http://localhost`) never shows that. `app/services/window-zoom-level.ts` writes the live level to electron-conf `ZOOM_LEVEL` on close, `before-quit` and before every cross-document navigation (a reload drops the temporary level). The zoom shortcuts (Cmd/Ctrl and +/−/0, numpad included) are a renderer key binding in `WorkspaceKeyboardShortcutsService` — the Windows/Linux window has no menu (`setMenu(null)`) — calling the synchronous preload-local bridge method `adjustZoomLevel`, which steps the same frame-bound level (`stepZoomLevel` in `libs/shared/interfaces`: 0.5 per press like Electron's `zoomIn`/`zoomOut` roles, clamped to levels −4…6); on macOS the renderer's `preventDefault()` keeps the menu role from stepping a second time. Contract: `docs/architecture/workspace-shell.md`, "Zoom level"
+- Persists the app zoom level (issue #1109): the preload restores it with `webFrame.setZoomLevel` (temporary, frame-bound zoom; level answered over the synchronous `WINDOW:GET_ZOOM_LEVEL` IPC, applied at `DOMContentLoaded` and acknowledged with `WINDOW:ZOOM_LEVEL_APPLIED` — any earlier `webFrame.setZoomLevel` leaves a hidden Linux/Windows window without `ready-to-show`), never `webContents.setZoomLevel` — under `file://` Chromium keys zoom by the full URL, so the app's path routing would reset it on the next resize after a section change, and dev mode (`http://localhost`) never shows that. `app/services/window-zoom-level.ts` writes the live level to electron-conf `ZOOM_LEVEL` on close, `before-quit` and before every cross-document navigation (a reload drops the temporary level). The zoom shortcuts (Cmd/Ctrl and +/−/0, numpad included) are a renderer key binding in `WorkspaceKeyboardShortcutsService` — the Windows/Linux window has no menu (`setMenu(null)`) — calling the synchronous preload-local bridge method `adjustZoomLevel`, which steps the same frame-bound level (`stepZoomLevel` in `libs/shared/interfaces`: 0.5 per press like Electron's `zoomIn`/`zoomOut` roles, clamped to levels −4…6, a stored level already outside them never moved against the request, so the returned level is not itself guaranteed in range); on macOS the renderer's `preventDefault()` keeps the menu role from stepping a second time. Contract: `docs/architecture/workspace-shell.md`, "Zoom level"
 - Holds a single-instance lock (`app/services/single-instance.ts`), requested after the `userData` override so E2E runs with their own data dir keep independent locks. A second launch quits and focuses the running window; concurrent instances would otherwise share a Chromium profile whose IndexedDB only one of them can lock, silently breaking renderer-side settings persistence. `IPTVNATOR_ALLOW_MULTIPLE_INSTANCES=1` opts out for local debugging. The guard also forwards that launch's argv and working directory, so `iptvnator playlist.m3u` against a running app opens the playlist instead of being discarded.
 
 **Database**:

libs/shared/interfaces/src/lib/electron-api.interface.ts

@@ -723,10 +723,13 @@ export interface ElectronBridgeApi {
      * Zoom shortcuts (Cmd/Ctrl and +/−/0). Synchronous and preload-local:
      * steps the FRAME-BOUND temporary zoom level through `webFrame` (never a
      * main-process `webContents.setZoomLevel`, whose per-URL entry the app's
-     * `file://` path routing resets — issue #1109), clamped to
-     * `ZOOM_LEVEL_MIN..ZOOM_LEVEL_MAX`, and returns the level now applied.
-     * Persistence needs nothing from the caller: the main process reads the
-     * live level back on close, quit and reload.
+     * `file://` path routing resets — issue #1109) by `stepZoomLevel`'s
+     * rules — one `ZOOM_LEVEL_STEP` inside `ZOOM_LEVEL_MIN..ZOOM_LEVEL_MAX`,
+     * a stored level already outside them never moved against the request —
+     * and returns the level now applied, which is therefore not itself
+     * guaranteed to be within the limits. Persistence needs nothing from the
+     * caller: the main process reads the live level back on close, quit and
+     * reload.
      */
     adjustZoomLevel: (action: ZoomLevelAction) => number;
     getWindowState: () => Promise<ElectronBridgeWindowState>;