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/lib/types.ts

@@ -175,6 +175,23 @@ export interface ConflictFile {
   theirs_size: number | null;
 }
 
+export interface GitBlameLine {
+  line_number: number;
+  content: string;
+  commit_hash: string;
+  short_hash: string;
+  author_name: string;
+  author_email: string;
+  author_time: number;
+  summary: string;
+  is_uncommitted: boolean;
+}
+
+export interface GitBlameResult {
+  path: string;
+  lines: GitBlameLine[];
+}
+
 export interface StoredCredential {
   username: string;
   password: string;