refactor: detect platform via APIService.isMobile() instead of Platform.isDesktopApp

Address the maintainer review on #949: determine the platform through the
plugin's own service layer (services.API.isMobile()) rather than Obsidian's
Platform API directly, matching the existing call in ObsidianLiveSyncSettingTab.
Applies to both PR-introduced sites: the runtime guard (ModuleObsidianEvents)
and the settings-pane toggle (PaneSyncSettings).

The TFile import becomes type-only so deps.ts is no longer pulled at runtime;
the unit test drives the platform through the services.API.isMobile() mock.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/modules/features/SettingDialogue/PaneSyncSettings.ts

@@ -11,7 +11,6 @@ import { EVENT_REQUEST_COPY_SETUP_URI, eventHub } from "../../../common/events.t
 import type { ObsidianLiveSyncSettingTab } from "./ObsidianLiveSyncSettingTab.ts";
 import type { PageFunctions } from "./SettingPane.ts";
 import { visibleOnly } from "./SettingPane.ts";
-import { Platform } from "../../../deps.ts";
 export function paneSyncSettings(
     this: ObsidianLiveSyncSettingTab,
     paneEl: HTMLElement,
@@ -193,7 +192,7 @@ export function paneSyncSettings(
         // Desktop app only, and only for the sync modes that keep a background replication channel
         // (LiveSync and Periodic). Ignored on mobile, where suspending preserves battery. The
         // visibility predicate mirrors the runtime guard in ModuleObsidianEvents.
-        if (Platform.isDesktopApp) {
+        if (!this.services.API.isMobile()) {
             new Setting(paneEl).setClass("wizardHidden").autoWireToggle("keepReplicationActiveInBackground", {
                 onUpdate: visibleOnly(
                     () => this.isConfiguredAs("syncMode", "LIVESYNC") || this.isConfiguredAs("syncMode", "PERIODIC")