feat(blame): add file blame dialog with git porcelain parsing

This change introduces a new backend command to fetch file blame using
git's line-porcelain output and returns structured per-line metadata.
The UI adds a BlameDialog that groups lines by commit, highlights
uncommitted changes, and styles the dialog to match the updated theme.

- Add get_file_blame command and parsing with uncommitted detection
- Wire BlameDialog into the explorer file node actions
- Add blame UI component and supporting types and styles

src/App.svelte

@@ -7,6 +7,7 @@
   import TitleBar from "./lib/TitleBar.svelte";
   import AiSettingsDialog from "./lib/components/AiSettingsDialog.svelte";
   import BranchDeleteConfirmDialog from "./lib/components/BranchDeleteConfirmDialog.svelte";
+  import BlameDialog from "./lib/components/BlameDialog.svelte";
   import BranchPanel from "./lib/components/BranchPanel.svelte";
   import CloneRepositoryDialog from "./lib/components/CloneRepositoryDialog.svelte";
   import CommitPanel from "./lib/components/CommitPanel.svelte";
@@ -50,6 +51,7 @@
     diffFileAgainstWorkingTree,
     compareFileToParent,
     fetchRemote,
+    getFileBlame,
     getStatus,
     lastCommitMessage,
     listBranches,
@@ -97,6 +99,7 @@
     ConflictFile,
     ExplorerNode,
     ExplorerNodeKind,
+    GitBlameLine,
     GitBranch as GitBranchInfo,
     GitCommit,
     GitCommitFile,
@@ -218,6 +221,11 @@
   let linePatchText = "";
   let linePatchLoading = false;
   let linePatchError = "";
+  let blameOpen = false;
+  let blameFilePath = "";
+  let blameLines: GitBlameLine[] = [];
+  let blameLoading = false;
+  let blameError = "";
   let pendingDiscard: PendingDiscard | null = null;
   let globalSearchOpen = false;
   let lastSearchQuery = "";
@@ -1921,6 +1929,33 @@
     linePatchError = "";
   }
 
+  async function openBlame(node: ExplorerNode) {
+    if (!activeRepoPath || node.kind !== "file") return;
+    blameOpen = true;
+    blameFilePath = node.path;
+    blameLines = [];
+    blameError = "";
+    blameLoading = true;
+
+    try {
+      const result = await getFileBlame(activeRepoPath, node.path);
+      blameLines = result.lines;
+    } catch (error) {
+      blameError = errorToMessage(error);
+      errorMessage = blameError;
+    } finally {
+      blameLoading = false;
+    }
+  }
+
+  function closeBlame() {
+    if (isBusy) return;
+    blameOpen = false;
+    blameFilePath = "";
+    blameLines = [];
+    blameError = "";
+  }
+
   function patchOperationLabel(action: PatchApplyAction, file: GitFileStatus): string {
     switch (action) {
       case "stage":
@@ -2726,6 +2761,7 @@
           onCollapseAllFolders={collapseAllExplorerFolders}
           onSelectNode={selectExplorerNode}
           onOpenFile={openFileFromExplorer}
+          onBlame={openBlame}
         />
       </aside>
 
@@ -2886,6 +2922,17 @@
   />
 {/if}
 
+{#if blameOpen}
+  <BlameDialog
+    filePath={blameFilePath}
+    lines={blameLines}
+    {isBusy}
+    isLoading={blameLoading}
+    error={blameError}
+    onClose={closeBlame}
+  />
+{/if}
+
 {#if pendingDiscard}
   <DiscardConfirmDialog
     file={pendingDiscard.file}