feat: Add arbitrary directory project storage with registry system

This major update replaces the fixed `generations/` directory with support
for storing projects in any directory on the filesystem. Projects are now
tracked via a cross-platform registry system.

## New Features

### Project Registry (`registry.py`)
- Cross-platform registry storing project name-to-path mappings
- Platform-specific config locations:
  - Windows: %APPDATA%\autonomous-coder\projects.json
  - macOS: ~/Library/Application Support/autonomous-coder/projects.json
  - Linux: ~/.config/autonomous-coder/projects.json
- POSIX path format for cross-platform compatibility
- File locking for concurrent access safety (fcntl/msvcrt)
- Atomic writes via temp file + rename to prevent corruption
- Fixed Windows file locking issue with tempfile.mkstemp()

### Filesystem Browser API (`server/routers/filesystem.py`)
- REST endpoints for browsing directories server-side
- Cross-platform support with blocked system paths:
  - Windows: C:\Windows, Program Files, ProgramData, etc.
  - macOS: /System, /Library, /private, etc.
  - Linux: /etc, /var, /usr, /bin, etc.
- Universal blocked paths: .ssh, .aws, .gnupg, .docker, etc.
- Hidden file detection (Unix dot-prefix + Windows attributes)
- UNC path blocking for security
- Windows drive enumeration via ctypes
- Directory creation with validation
- Added `has_children` field to DirectoryEntry schema

### UI Folder Browser (`ui/src/components/FolderBrowser.tsx`)
- React component for selecting project directories
- Breadcrumb navigation with clickable segments
- Windows drive selector
- New folder creation inline
- Fixed text visibility with explicit color values

## Updated Components

### Server Routers
- `projects.py`: Uses registry instead of fixed generations/ directory
- `agent.py`: Uses registry for project path lookups
- `features.py`: Uses registry for database path resolution
- `spec_creation.py`: Uses registry for WebSocket project resolution

### Process Manager (`server/services/process_manager.py`)
- Fixed sandbox issue: subprocess now uses project_dir as cwd
- This allows the Claude SDK sandbox to access external project directories

### Schemas (`server/schemas.py`)
- Added `has_children` to DirectoryEntry
- Added `in_progress` to ProjectStats
- Added path field to ProjectSummary and ProjectDetail

### UI Components
- `NewProjectModal.tsx`: Multi-step wizard with folder selection
- Added clarifying text about subfolder creation
- Fixed text color visibility issues

### API Client (`ui/src/lib/api.ts`)
- Added filesystem API functions (listDirectory, createDirectory)
- Fixed Windows path splitting for directory creation

### Documentation
- Updated CLAUDE.md with registry system details
- Updated command examples for absolute paths

## Security Improvements
- Blocked `.` and `..` in directory names to prevent traversal
- Added path blocking check in project creation
- UNC path blocking throughout filesystem API

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

ui/src/hooks/useProjects.ts

@@ -29,8 +29,8 @@ export function useCreateProject() {
   const queryClient = useQueryClient()
 
   return useMutation({
-    mutationFn: ({ name, specMethod }: { name: string; specMethod?: 'claude' | 'manual' }) =>
-      api.createProject(name, specMethod),
+    mutationFn: ({ name, path, specMethod }: { name: string; path: string; specMethod?: 'claude' | 'manual' }) =>
+      api.createProject(name, path, specMethod),
     onSuccess: () => {
       queryClient.invalidateQueries({ queryKey: ['projects'] })
     },
@@ -170,3 +170,33 @@ export function useHealthCheck() {
     retry: false,
   })
 }
+
+// ============================================================================
+// Filesystem
+// ============================================================================
+
+export function useListDirectory(path?: string) {
+  return useQuery({
+    queryKey: ['filesystem', 'list', path],
+    queryFn: () => api.listDirectory(path),
+  })
+}
+
+export function useCreateDirectory() {
+  const queryClient = useQueryClient()
+
+  return useMutation({
+    mutationFn: (path: string) => api.createDirectory(path),
+    onSuccess: (_, path) => {
+      // Invalidate parent directory listing
+      const parentPath = path.split('/').slice(0, -1).join('/') || undefined
+      queryClient.invalidateQueries({ queryKey: ['filesystem', 'list', parentPath] })
+    },
+  })
+}
+
+export function useValidatePath() {
+  return useMutation({
+    mutationFn: (path: string) => api.validatePath(path),
+  })
+}