Add repository opening loading overlay

Introduce a full-screen, animated overlay to provide visual feedback
when the application is opening a repository. This prevents perceived
delays and informs the user about the ongoing operation.

Also, enhance build performance and binary size by configuring
Cargo profiles:
- Development: Enable incremental compilation, use line-tables-only
  debug info, and optimize third-party dependencies to speed up
  rebuilds and improve runtime snappiness during development.
- Release: Apply aggressive optimizations (opt-level 3, thin LTO,
  single codegen unit, stripping) for smaller, faster binaries.

src/App.svelte

@@ -14,6 +14,7 @@
   import FileHistoryPanel from "./lib/components/FileHistoryPanel.svelte";
   import GlobalSearchDialog from "./lib/components/GlobalSearchDialog.svelte";
   import HistoryPanel from "./lib/components/HistoryPanel.svelte";
+  import RepoLoadingOverlay from "./lib/components/RepoLoadingOverlay.svelte";
   import ResolveDialog from "./lib/components/ResolveDialog.svelte";
   import StatusPanel from "./lib/components/StatusPanel.svelte";
   import UpdateToast from "./lib/components/UpdateToast.svelte";
@@ -133,6 +134,8 @@
 
   $: isBusy = operation.length > 0;
   $: hasRepository = activeRepoPath.length > 0 && status !== null;
+  $: openingRepo = operation === "Opening repository";
+  $: repoDisplayName = ((repoPath || activeRepoPath).split(/[\\/]/).filter(Boolean).pop()) ?? "";
   $: changedFiles = status?.files ?? [];
   $: stagedCount = status?.files.filter((f) => f.staged !== null).length ?? 0;
   $: unstagedCount = status?.files.filter((f) => f.unstaged !== null).length ?? 0;
@@ -1207,6 +1210,11 @@
   />
 {/if}
 
+<!-- Full-screen overlay while a repository is being opened -->
+{#if openingRepo}
+  <RepoLoadingOverlay repoName={repoDisplayName} />
+{/if}
+
 <!-- Conflict resolve dialog -->
 {#if resolveDialogOpen}
   <ResolveDialog