feat(history): add visible-parent resolver and status optimizations

Introduce an iterative visibleParentResolver for commit-graph rendering,
replacing a recursive traversal. It preserves first-parent ordering,
deduplicates converging paths, and avoids stack overflows; a test suite
validates correctness and performance. Additionally, streamline background
fetch handling in the UI to reuse fetchRemote's returned status and avoid
unnecessary status reads and tab invalidation, and refactor Git status
handling in Rust to build a file_status_index that preserves rename and
first-match semantics while speeding lookups.

- Add visibleParentResolver + comprehensive tests for ancestry handling
- Reuse fetchRemote result to apply status and skip unchanged updates
- Replace status_for_file with file_status_index to improve performance

src/lib/components/HistoryPanel.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
   import { Cherry, ChevronDown, ChevronRight, CloudOff, EllipsisVertical, GitBranch, GitMerge, LoaderCircle, RotateCcw, StickyNote, Tag, X } from "@lucide/svelte";
+  import { visibleParentResolver } from "../graphParents";
   import type { FileStatusKind, GitCommit, GitCommitFile } from "../types";
 
   interface GraphSegment {
@@ -338,25 +339,6 @@
     return branchesAreVisible(row?.branchLabels ?? []);
   }
 
-  function nearestVisibleGraphParents(
-    hash: string,
-    visibleHashes: Set<string>,
-    commitByHash: Map<string, GitCommit>,
-    seen: Set<string>,
-  ): string[] {
-    if (visibleHashes.has(hash)) return [hash];
-    if (seen.has(hash)) return [];
-    seen.add(hash);
-
-    const commit = commitByHash.get(hash);
-    if (!commit) return [];
-    return uniqueStrings(
-      commit.parents.flatMap((parentHash) => (
-        nearestVisibleGraphParents(parentHash, visibleHashes, commitByHash, new Set(seen))
-      )),
-    );
-  }
-
   function branchMembershipByHash(items: GitCommit[]): Map<string, string[]> {
     const commitByHash = new Map(items.map((commit) => [commit.hash, commit]));
     const membership = new Map<string, Set<string>>();
@@ -395,12 +377,12 @@
   function visibleCommitEntriesForGraph(items: GitCommit[], branchMembership: Map<string, string[]>): VisibleCommitEntry[] {
     const visibleItems = items.filter((commit) => branchesAreVisible(branchMembership.get(commit.hash) ?? []));
     const visibleHashes = new Set(visibleItems.map((commit) => commit.hash));
-    const commitByHash = new Map(items.map((commit) => [commit.hash, commit]));
+    const resolveParents = visibleParentResolver(items, visibleHashes);
 
     return visibleItems.map((commit) => {
       const parents = uniqueStrings(
         commit.parents.flatMap((parentHash) => (
-          nearestVisibleGraphParents(parentHash, visibleHashes, commitByHash, new Set())
+          resolveParents(parentHash)
         )),
       );
       return { commit, graphCommit: { ...commit, parents } };