feat: add repository workspace as default project view

- Create git file utilities (list_tree, get_file_content, list_branches, commit_file)
- Add file browsing API endpoints (list, content, branches, update)
- Create RepoWorkspace page with sidebar + main content layout
- Add FileTree component with directory navigation
- Add FileViewer component for viewing file contents
- Update project list to link to workspace
- Add workspace CSS styles
- Update router with workspace route

Quality gates: ruff ✓, mypy ✓, typecheck ✓, build ✓

openspec/changes/archive/2026-05-19-git-history-visualization/proposal.md

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+# Git History Visualization
+
+## Problem
+
+Currently, users can create and manage git repositories, but they have no way to view the commit history, branches, or understand the repository structure. This makes it impossible to:
+- See what commits exist in a repository
+- Understand branch relationships and merges
+- View commit details (message, author, date, changes)
+- Explore the repository's evolution over time
+
+## Solution
+
+Build an interactive git history visualization similar to GitKraken that provides:
+1. **Graph View**: Visual commit graph showing branches, merges, and commit relationships
+2. **List View**: Linear commit log with details
+3. **Commit Details**: Click any commit to see full details and diff
+4. **Branch Visualization**: See all branches and their relationships
+
+## Benefits
+
+- **Understand repository structure** at a glance
+- **Track changes** and see who made what changes when
+- **Navigate history** easily without using command line
+- **Review code** by examining commit diffs
+
+## Scope
+
+### What we're building:
+- Backend API to extract git history from bare/mirror repos using git CLI
+- Graph visualization component (SVG-based commit graph)
+- List view component (linear commit log)
+- Commit detail panel (message, author, date, diff)
+- View toggle (graph vs list)
+- Branch label display
+
+### Out of scope (future enhancements):
+- Interactive branch operations (checkout, merge, rebase)
+- Tag management
+- File browser at specific commits
+- Blame/annotation view
+- Advanced filtering/search
+
+## Technical Approach
+
+**Backend**: Execute `git log --graph --format=...` commands to get structured commit data
+**Frontend**: Custom SVG rendering for graph, React components for list view and details panel