refactor(ui): modernize status bar and component structure

This commit introduces a comprehensive overhaul of the application's UI, focusing on modernizing the global workspace status bar and improving overall theming consistency. Several components were refactored to simplify prop handling and improve separation of concerns, particularly within the TitleBar and RepoToolbar. The CSS includes extensive new variables and styles for better visual fidelity across light and dark themes.

- Overhauled the main application footer to display version, branch status, and sync metrics.
- Added global CSS variables and component styling for a modern look.
- Simplified repository state management by removing redundant props from TitleBar.

src/lib/components/CompareDialog.svelte

@@ -10,6 +10,12 @@
         rightNum?: number; rightText?: string; rightKind: "add" | "context" | "empty";
       };
 
+  interface DiffMarker {
+    start: number;
+    end: number;
+    kind: "add" | "delete" | "mixed";
+  }
+
   interface Props {
     comparison: GitCommitComparison;
     selectedDiffPath: string;
@@ -173,10 +179,40 @@
     return rows;
   }
 
+  function buildDiffMarkers(rows: SplitRow[]): DiffMarker[] {
+    const markers: DiffMarker[] = [];
+    let current: DiffMarker | null = null;
+    for (let index = 0; index < rows.length; index++) {
+      const row = rows[index];
+      if (row.type !== "pair" || (row.leftKind === "context" && row.rightKind === "context")) {
+        current = null;
+        continue;
+      }
+      const kind = row.leftKind === "del" && row.rightKind === "add"
+        ? "mixed"
+        : row.rightKind === "add" ? "add" : "delete";
+      if (current && current.end === index - 1 && current.kind === kind) {
+        current.end = index;
+      } else {
+        current = { start: index, end: index, kind };
+        markers.push(current);
+      }
+    }
+    return markers;
+  }
+
+  function scrollToDiffMarker(rowIndex: number) {
+    const ratio = rowIndex / Math.max(splitRows.length - 1, 1);
+    for (const pane of [beforePane, afterPane]) {
+      if (pane) pane.scrollTop = ratio * Math.max(pane.scrollHeight - pane.clientHeight, 0);
+    }
+  }
+
   let diffByPath      = $derived(buildDiffByPath(comparison.patch));
   let selectedFile    = $derived(comparison.files.find((f) => f.path === selectedDiffPath) ?? null);
   let selectedPatch   = $derived(selectedFile ? (diffByPath.get(selectedFile.path) ?? "") : "");
   let splitRows       = $derived(buildSplitRows(selectedPatch));
+  let diffMarkers     = $derived(buildDiffMarkers(splitRows));
 </script>
 
 <div
@@ -262,6 +298,7 @@
             </div>
 
             <!-- Split diff grid -->
+            <div class="split-diff-shell">
             <div class="split-diff" role="table" aria-label="Side-by-side diff">
               <div
                 class="split-pane"
@@ -298,6 +335,19 @@
                 </div>
               </div>
             </div>
+            <nav class="diff-overview" aria-label="Change overview">
+              {#each diffMarkers as marker, index (`${marker.start}-${marker.end}-${marker.kind}`)}
+                <button
+                  class="diff-overview-marker {marker.kind}"
+                  type="button"
+                  style={`--marker-position: ${(marker.start / Math.max(splitRows.length - 1, 1)) * 100}%`}
+                  onclick={() => scrollToDiffMarker(marker.start)}
+                  title={`Jump to change ${index + 1} of ${diffMarkers.length}`}
+                  aria-label={`Jump to change ${index + 1} of ${diffMarkers.length}`}
+                ></button>
+              {/each}
+            </nav>
+            </div>
           {/if}
         </div>