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>

server/schemas.py

@@ -17,12 +17,14 @@ from pydantic import BaseModel, Field
 class ProjectCreate(BaseModel):
     """Request schema for creating a new project."""
     name: str = Field(..., min_length=1, max_length=50, pattern=r'^[a-zA-Z0-9_-]+$')
+    path: str = Field(..., min_length=1, description="Absolute path to project directory")
     spec_method: Literal["claude", "manual"] = "claude"
 
 
 class ProjectStats(BaseModel):
     """Project statistics."""
     passing: int = 0
+    in_progress: int = 0
     total: int = 0
     percentage: float = 0.0
 
@@ -30,6 +32,7 @@ class ProjectStats(BaseModel):
 class ProjectSummary(BaseModel):
     """Summary of a project for list view."""
     name: str
+    path: str
     has_spec: bool
     stats: ProjectStats
 
@@ -37,6 +40,7 @@ class ProjectSummary(BaseModel):
 class ProjectDetail(BaseModel):
     """Detailed project information."""
     name: str
+    path: str
     has_spec: bool
     stats: ProjectStats
     prompts_dir: str
@@ -151,3 +155,48 @@ class WSAgentStatusMessage(BaseModel):
     """WebSocket message for agent status changes."""
     type: Literal["agent_status"] = "agent_status"
     status: str
+
+
+# ============================================================================
+# Filesystem Schemas
+# ============================================================================
+
+class DriveInfo(BaseModel):
+    """Information about a drive (Windows only)."""
+    letter: str
+    label: str
+    available: bool = True
+
+
+class DirectoryEntry(BaseModel):
+    """An entry in a directory listing."""
+    name: str
+    path: str  # POSIX format
+    is_directory: bool
+    is_hidden: bool = False
+    size: int | None = None  # Bytes, for files
+    has_children: bool = False  # True if directory has subdirectories
+
+
+class DirectoryListResponse(BaseModel):
+    """Response for directory listing."""
+    current_path: str  # POSIX format
+    parent_path: str | None
+    entries: list[DirectoryEntry]
+    drives: list[DriveInfo] | None = None  # Windows only
+
+
+class PathValidationResponse(BaseModel):
+    """Response for path validation."""
+    valid: bool
+    exists: bool
+    is_directory: bool
+    can_read: bool
+    can_write: bool
+    message: str = ""
+
+
+class CreateDirectoryRequest(BaseModel):
+    """Request to create a new directory."""
+    parent_path: str
+    name: str = Field(..., min_length=1, max_length=255)