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/repo-workspace/proposal.md

@@ -0,0 +1,72 @@
+# Repository Workspace - Default Project View
+
+## Problem
+
+Currently, clicking on a project shows a generic placeholder. Users need to navigate to repositories separately. There's no easy way to browse repository files or see project content at a glance.
+
+## Solution
+
+Create a **Repository Workspace** as the default project view that provides:
+
+1. **File browser** for repositories - browse files and directories
+2. **Branch selector** - switch between branches
+3. **Mini file viewer** - view file contents with syntax highlighting
+4. **Quick edit capability** - small edits without leaving the browser
+5. **Repository overview** - see all repos in the project
+
+This becomes the default view when clicking on a project, making the project the central workspace.
+
+## Key Features
+
+### Default Project View
+- Clicking any project opens the repository workspace
+- Shows first repo by default (or repo selector if multiple)
+- File browser on the left, content viewer on the right
+
+### File Browser
+- Tree view of repository files and directories
+- Expandable/collapsible folders
+- Click file to view contents
+- Breadcrumb navigation
+
+### Branch Management
+- Branch selector dropdown
+- Shows current branch
+- Lists all branches (local + remote)
+- Switch branches to view different states
+
+### File Viewer
+- Syntax highlighting for common file types
+- Line numbers
+- View mode (read-only by default)
+- Edit mode toggle for small changes
+
+### Repository Navigation
+- List all repositories in the project
+- Quick switch between repos
+- Repository cards with metadata (last commit, branch count)
+
+## Benefits
+
+- **Central hub**: Project becomes the main workspace, not just a container
+- **Quick access**: See code immediately without extra clicks
+- **Contextual**: Browse files while viewing commit history
+- **Familiar**: Similar to GitHub/GitLab file browser
+
+## Scope
+
+### What stays:
+- Existing repository list page (moves to sub-page)
+- Git history visualization
+- Repository creation/deletion
+
+### What's new:
+- Repository workspace page (default project view)
+- File browser component
+- File viewer component
+- Branch selector component
+- API endpoints for file operations
+
+### What's changed:
+- Project list items become clickable links
+- Default project route shows workspace instead of placeholder