fix: resolve four frontend/backend issues

- Fix ProjectsPage tests by wrapping renders in MemoryRouter (9 passing)
- Improve session auto-naming to 'project / repo / tool' format
- Add missing /users/me/sessions endpoint for sidebar session loading
- Handle git history 500s: catch RuntimeError in endpoints, graceful empty repo handling
- Add git status badge and discard-changes button to FileEditor toolbar

Quality gates: tsc pass, build pass, Python syntax pass

apps/api/src/utils/git_history.py

@@ -60,9 +60,12 @@ def get_commit_history(repo_path: str, branch: str | None = None, limit: int = 1
 
     Returns structured data including commits, branches, and graph information.
     """
-    # Get list of branches
-    branches_output = _run_git_command(repo_path, ["branch", "-a", "--format=%(refname:short)"])
-    branches = [b.strip() for b in branches_output.strip().split("\n") if b.strip()]
+    # Get list of branches (may fail for empty repos)
+    try:
+        branches_output = _run_git_command(repo_path, ["branch", "-a", "--format=%(refname:short)"])
+        branches = [b.strip() for b in branches_output.strip().split("\n") if b.strip()]
+    except RuntimeError:
+        branches = []
 
     # Build git log command - use NULL bytes as separators to avoid parsing issues
     log_args = [
@@ -76,7 +79,16 @@ def get_commit_history(repo_path: str, branch: str | None = None, limit: int = 1
     else:
         log_args.append("--all")
 
-    log_output = _run_git_command(repo_path, log_args)
+    try:
+        log_output = _run_git_command(repo_path, log_args)
+    except RuntimeError:
+        # Empty repo or no commits
+        return {
+            "commits": [],
+            "branches": branches,
+            "total_commits": 0,
+            "graph_data": {"nodes": [], "edges": []},
+        }
 
     # Get branch info for each commit
     branch_map = _get_branch_map(repo_path)
@@ -113,8 +125,11 @@ def get_commit_history(repo_path: str, branch: str | None = None, limit: int = 1
         )
 
     # Get total commit count
-    count_output = _run_git_command(repo_path, ["rev-list", "--all", "--count"])
-    total_commits = int(count_output.strip()) if count_output.strip() else 0
+    try:
+        count_output = _run_git_command(repo_path, ["rev-list", "--all", "--count"])
+        total_commits = int(count_output.strip()) if count_output.strip() else 0
+    except RuntimeError:
+        total_commits = 0
 
     # Build graph data and generate graph symbols
     graph_data = _build_graph_data(commits)