feat: add git history visualization frontend

- Add API client functions for commit history and detail endpoints
- Create GitHistoryPage with commit list, graph visualization, and detail panel
- Add branch selector for viewing different branches
- Integrate history view into repository list with History button
- Add comprehensive CSS styles for history page layout

Quality gates: typecheck ✓, lint ✓, build ✓

apps/web/src/api/git_repositories.ts

@@ -49,3 +49,61 @@ export async function createRepository(
 export async function deleteRepository(projectId: string, repoId: string): Promise<void> {
   await apiClient.delete(`/projects/${projectId}/repositories/${repoId}`);
 }
+
+export interface CommitHistoryEntry {
+  hash: string;
+  short_hash: string;
+  message: string;
+  author_name: string;
+  author_email: string;
+  author_date: string;
+  refs: string[];
+  graph_symbol: string;
+  graph_depth: number;
+}
+
+export interface CommitHistoryResponse {
+  commits: CommitHistoryEntry[];
+  branches: string[];
+  tags: string[];
+}
+
+export async function getRepositoryHistory(
+  projectId: string,
+  repoId: string,
+  branch?: string
+): Promise<CommitHistoryResponse> {
+  const params = branch ? `?branch=${encodeURIComponent(branch)}` : "";
+  const response = await apiClient.get(`/projects/${projectId}/repositories/${repoId}/history${params}`);
+  return response.data;
+}
+
+export interface CommitDetail {
+  hash: string;
+  short_hash: string;
+  message: string;
+  author_name: string;
+  author_email: string;
+  author_date: string;
+  committer_name: string;
+  committer_email: string;
+  committer_date: string;
+  stats: {
+    additions: number;
+    deletions: number;
+    files_changed: number;
+  };
+  diff: string;
+  parents: string[];
+}
+
+export async function getCommitDetail(
+  projectId: string,
+  repoId: string,
+  commitHash: string
+): Promise<CommitDetail> {
+  const response = await apiClient.get(
+    `/projects/${projectId}/repositories/${repoId}/commits/${commitHash}`
+  );
+  return response.data;
+}