Implement CLI commands and utility functions for MVP-1

- Add complete CLI command implementations with Typer subcommands
- Implement utils/time.py with duration formatting and datetime utilities
- Implement utils/path.py with project path management utilities
- Wire up all commands to main CLI entry point

tracker/utils/path.py

@@ -1 +1,87 @@
 """Path utility functions."""
+
+from pathlib import Path
+from typing import Optional
+
+
+def ensure_dir(path: Path) -> Path:
+    """Ensure a directory exists, creating it if necessary.
+
+    Args:
+        path: Path to the directory.
+
+    Returns:
+        The path to the directory.
+    """
+    path.mkdir(parents=True, exist_ok=True)
+    return path
+
+
+def project_root(slug: str, projects_root: Optional[Path] = None) -> Path:
+    """Get the root path for a project.
+
+    Args:
+        slug: Project slug.
+        projects_root: Root directory for all projects. Defaults to ./projects.
+
+    Returns:
+        Path to the project root.
+    """
+    if projects_root is None:
+        projects_root = Path("projects")
+    return projects_root / slug
+
+
+def relative_to_project(slug: str, relative_path: str, projects_root: Optional[Path] = None) -> Path:
+    """Get a path relative to a project.
+
+    Args:
+        slug: Project slug.
+        relative_path: Relative path within the project.
+        projects_root: Root directory for all projects.
+
+    Returns:
+        Absolute path to the file within the project.
+    """
+    root = project_root(slug, projects_root)
+    return root / relative_path
+
+
+def is_within_project(slug: str, file_path: Path, projects_root: Optional[Path] = None) -> bool:
+    """Check if a file path is within a project.
+
+    Args:
+        slug: Project slug.
+        file_path: Path to check.
+        projects_root: Root directory for all projects.
+
+    Returns:
+        True if file_path is within the project directory.
+    """
+    project_path = project_root(slug, projects_root)
+    try:
+        file_path.resolve().relative_to(project_path.resolve())
+        return True
+    except ValueError:
+        return False
+
+
+def sanitize_filename(filename: str) -> str:
+    """Sanitize a filename by removing invalid characters.
+
+    Args:
+        filename: Original filename.
+
+    Returns:
+        Sanitized filename safe for file system use.
+    """
+    # Remove or replace invalid characters
+    invalid_chars = '<>:"/\\|?*'
+    for char in invalid_chars:
+        filename = filename.replace(char, "_")
+
+    # Limit length
+    if len(filename) > 255:
+        filename = filename[:255]
+
+    return filename