Improve global search: Add diffing from results with query highlighting

Users can now open a diff for a specific search hit directly from the global search results. The original search query will be highlighted within the diff view, making it easier to locate the relevant changes.

Additionally, add `--no-textconv` to git commands used in search and diff operations. This prevents failures when git encounters binary files that textconv drivers might otherwise attempt to process.

src/lib/components/GlobalSearchDialog.svelte

@@ -1,5 +1,5 @@
 <script lang="ts">
-  import { CalendarDays, FileCode, LoaderCircle, Search, User, X } from "@lucide/svelte";
+  import { CalendarDays, FileCode, GitCompare, LoaderCircle, Search, User, X } from "@lucide/svelte";
   import type { GitSearchHit } from "../types";
 
   interface Props {
@@ -11,6 +11,7 @@
     onClose: () => void;
     onSearch: (query: string, caseSensitive: boolean, limit: number) => void | Promise<void>;
     onCancel: () => void | Promise<void>;
+    onDiff: (hit: GitSearchHit) => void | Promise<void>;
   }
 
   let {
@@ -22,6 +23,7 @@
     onClose = () => {},
     onSearch = () => {},
     onCancel = () => {},
+    onDiff = () => {},
   }: Props = $props();
 
   let query = $state("");
@@ -148,6 +150,16 @@
                   {#if hit.matches_added > 1}
                     <span class="pill pill-active">+{hit.matches_added} matches</span>
                   {/if}
+                  <button
+                    class="btn-secondary search-hit-diff"
+                    type="button"
+                    disabled={isBusy}
+                    title={`Compare this version of ${hit.file} with the current version`}
+                    onclick={() => onDiff(hit)}
+                  >
+                    <GitCompare size={14} aria-hidden="true" />
+                    DIFF
+                  </button>
                 </header>
 
                 <div class="search-hit-meta">