Only allow Tauri imports in the desktop app (#5995)

# Description of Changes
Adds an eslint rule to disallow importing any Tauri APIs outside the
desktop folder to help hint to developers that they should be following
the frontend architecture.

While doing this, I also discovered that you can provide a custom
message in the `no-restricted-imports` rule, which is nicer than the
comments that I'd previously added to the eslint config file to explain
why they weren't allowed:

```text
/Users/jamesbrunton/Dev/spdf1/frontend/src/core/components/shared/config/configSections/GeneralSection.tsx
  19:1  error  'src/core/contexts/PreferencesContext' import is restricted from being used by a pattern. Use @app/* imports instead of absolute src/ imports              no-restricted-imports
  20:1  error  '../../../../../core/contexts/AppConfigContext' import is restricted from being used by a pattern. Use @app/* imports instead of relative imports          no-restricted-imports
  21:1  error  '@tauri-apps/core' import is restricted from being used by a pattern. Tauri APIs are desktop-only. Review frontend/DeveloperGuide.md for structure advice  no-restricted-imports
```

frontend/src/core/components/shared/config/configSections/GeneralSection.tsx

@@ -1,4 +1,4 @@
-import React, { useState, useEffect, useMemo } from "react";
+import React, { useState, useEffect } from "react";
 import {
   Paper,
   Stack,
@@ -22,8 +22,7 @@ import type { ToolPanelMode } from "@app/constants/toolPanel";
 import LocalIcon from "@app/components/shared/LocalIcon";
 import { updateService, UpdateSummary } from "@app/services/updateService";
 import UpdateModal from "@app/components/shared/UpdateModal";
-import { getVersion } from "@tauri-apps/api/app";
-import { isTauri } from "@tauri-apps/api/core";
+import { useFrontendVersionInfo } from "@app/hooks/useFrontendVersionInfo";
 
 const DEFAULT_AUTO_UNZIP_FILE_LIMIT = 4;
 const BANNER_DISMISSED_KEY = "stirlingpdf_features_banner_dismissed";
@@ -46,10 +45,8 @@ const GeneralSection: React.FC<GeneralSectionProps> = ({ hideTitle = false, hide
   const [updateSummary, setUpdateSummary] = useState<UpdateSummary | null>(null);
   const [updateModalOpened, setUpdateModalOpened] = useState(false);
   const [checkingUpdate, setCheckingUpdate] = useState(false);
-  const [mismatchVersion, setMismatchVersion] = useState(false);
-  const isTauriApp = useMemo(() => isTauri(), []);
-  const [appVersion, setAppVersion] = useState<string | null>(null);
-  const frontendVersionLabel = appVersion ?? t("common.loading", "Loading...");
+  const { appVersion, mismatchVersion } = useFrontendVersionInfo(config?.appVersion);
+  const frontendVersionLabel = appVersion ?? t("common.loading", "Loading..."); // null = loading, shown only when appVersion !== undefined
 
   // Sync local state with preference changes
   useEffect(() => {
@@ -91,52 +88,6 @@ const GeneralSection: React.FC<GeneralSectionProps> = ({ hideTitle = false, hide
     setCheckingUpdate(false);
   };
 
-  useEffect(() => {
-    if (!isTauriApp) {
-      setMismatchVersion(false);
-      return;
-    }
-
-    let cancelled = false;
-    const fetchFrontendVersion = async () => {
-      try {
-        const frontendVersion = await getVersion();
-        if (!cancelled) {
-          setAppVersion(frontendVersion);
-        }
-      } catch (error) {
-        console.error("[GeneralSection] Failed to fetch frontend version:", error);
-      }
-    };
-
-    fetchFrontendVersion();
-
-    return () => {
-      cancelled = true;
-    };
-  }, [isTauriApp]);
-
-  useEffect(() => {
-    if (!isTauriApp) {
-      return;
-    }
-
-    if (!appVersion || !config?.appVersion) {
-      setMismatchVersion(false);
-      return;
-    }
-
-    if (appVersion !== config.appVersion) {
-      console.warn("[GeneralSection] Mismatch between Tauri version and AppConfig version:", {
-        backendVersion: config.appVersion,
-        frontendVersion: appVersion,
-      });
-      setMismatchVersion(true);
-    } else {
-      setMismatchVersion(false);
-    }
-  }, [isTauriApp, appVersion, config?.appVersion]);
-
   // Check if login is disabled
   const loginDisabled = !config?.enableLogin;
 
@@ -239,7 +190,7 @@ const GeneralSection: React.FC<GeneralSectionProps> = ({ hideTitle = false, hide
                 )}
               </Group>
             </div>
-            {isTauriApp && (
+            {appVersion !== undefined && (
               <Group justify="space-between" align="center">
                 <div>
                   <Text size="sm" c="dimmed">

frontend/src/core/hooks/useFrontendVersionInfo.ts

@@ -0,0 +1,8 @@
+export interface FrontendVersionInfo {
+  appVersion: string | null | undefined; // undefined = not applicable, null = loading, string = loaded
+  mismatchVersion: boolean;
+}
+
+export function useFrontendVersionInfo(_backendVersion: string | undefined): FrontendVersionInfo {
+  return { appVersion: undefined, mismatchVersion: false };
+}

frontend/src/desktop/hooks/useFrontendVersionInfo.ts

@@ -0,0 +1,44 @@
+import { useState, useEffect } from "react";
+import { getVersion } from "@tauri-apps/api/app";
+import type { FrontendVersionInfo } from "@core/hooks/useFrontendVersionInfo";
+
+export function useFrontendVersionInfo(backendVersion: string | undefined): FrontendVersionInfo {
+  const [appVersion, setAppVersion] = useState<string | null>(null);
+  const [mismatchVersion, setMismatchVersion] = useState(false);
+
+  useEffect(() => {
+    let cancelled = false;
+    const fetchVersion = async () => {
+      try {
+        const version = await getVersion();
+        if (!cancelled) {
+          setAppVersion(version);
+        }
+      } catch (error) {
+        console.error("[useFrontendVersionInfo] Failed to fetch frontend version:", error);
+      }
+    };
+    fetchVersion();
+    return () => {
+      cancelled = true;
+    };
+  }, []);
+
+  useEffect(() => {
+    if (!appVersion || !backendVersion) {
+      setMismatchVersion(false);
+      return;
+    }
+    if (appVersion !== backendVersion) {
+      console.warn("[useFrontendVersionInfo] Mismatch between frontend version and AppConfig version:", {
+        backendVersion,
+        frontendVersion: appVersion,
+      });
+      setMismatchVersion(true);
+    } else {
+      setMismatchVersion(false);
+    }
+  }, [appVersion, backendVersion]);
+
+  return { appVersion, mismatchVersion };
+}