feat(workspace): persist workspace UI filters and disable drag-drop

Add a lightweight workspace preferences helper to store optional UI
settings in localStorage and integrate it with the issues views so
filters, queries, and view mode are restored per source. The
integration board now remembers repository and query filters, and the
Issue Center restores state filters and view mode across sessions.
Also disable drag and drop for the main Tauri window to avoid accidental
file drops.

- Add read/write helpers for workspace preferences in localStorage
- Persist and restore filters, queries, and view mode for issue views
- Disable window drag-and-drop to prevent accidental file drops

src/lib/components/IssueCenter.svelte

@@ -14,6 +14,7 @@
   import { issueTone, issueStateLabel } from "../issuePresentation";
   import IntegrationBoardView from "./IntegrationBoardView.svelte";
   import SelectMenu from "./SelectMenu.svelte";
+  import { readWorkspacePreferences, writeWorkspacePreferences } from "../workspacePreferences";
   import { listIntegrationIssues, closeIntegrationIssue, openInBrowser } from "../git";
   import { configuredIntegrationSources, integrationCredentialKey } from "../integrations";
   import type { GitIntegrationSettings, IntegrationIssue, StoredCredential } from "../types";
@@ -44,6 +45,7 @@
   let mounted = false;
   let generation = 0;
   let lastKey = "";
+  const preferenceKey = "gitty.issues.v1";
   $: de = language === "de";
   $: sources = configuredIntegrationSources(integrations);
   $: source = sources.find(item => item.id === sourceId) ?? sources[0];
@@ -56,11 +58,14 @@
     issues = saved?.issues ?? [];
     nextCursor = saved?.nextCursor ?? null;
     selectedId = "";
-    stateFilter = "";
-    repositoryFilter = "";
+    restoreFilters(sourceKey);
     error = "";
     if (source) void loadIssues();
   }
+  $: if (mounted && sourceKey && sourceKey === lastKey) {
+    writeWorkspacePreferences(preferenceKey, { sourceId: source?.id ?? "", viewMode });
+    writeWorkspacePreferences(`${preferenceKey}:${sourceKey}`, { stateFilter, repositoryFilter, query });
+  }
   $: normalizedQuery = query.trim().toLocaleLowerCase();
   $: filtered = issues.filter(issue => (!repositoryFilter || issue.repositoryName === repositoryFilter) && (!stateFilter || issue.state === stateFilter) &&
     `${issue.title} ${issue.number} ${issue.repositoryName} ${issue.author} ${issue.labels.join(" ")} ${issue.assignees.join(" ")}`.toLocaleLowerCase().includes(normalizedQuery));
@@ -71,6 +76,9 @@
   $: description = selected ? plainDescription(selected) : "";
 
   onMount(() => {
+    const saved = readWorkspacePreferences(preferenceKey);
+    sourceId = saved.sourceId ?? "";
+    viewMode = saved.viewMode === "board" ? "board" : "list";
     mounted = true;
     reduceMotion = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
     const closeDetailsOutside = (event: PointerEvent) => {
@@ -87,6 +95,13 @@
   });
   onDestroy(() => { generation++; });
 
+  function restoreFilters(key: string) {
+    const saved = readWorkspacePreferences(`${preferenceKey}:${key}`);
+    stateFilter = saved.stateFilter ?? "";
+    repositoryFilter = saved.repositoryFilter ?? "";
+    query = saved.query ?? "";
+  }
+
   async function withTimeout<T>(promise: Promise<T>, ms: number): Promise<T> {
     let timer: ReturnType<typeof setTimeout>;
     try {