Add browser-based exercises for Level 1 projects

[travisjneuman]

Description

Create optional browser-based versions of Level 1 projects that learners can try in an online Python environment (e.g., Replit, Google Colab, or PythonAnywhere) without needing a local setup.

Scope

• Create a browser/ directory inside projects/level-1/ with links or notebooks
• Focus on the 5 most popular projects: 01-input-validator-lab, 02-password-strength-checker, 05-csv-first-reader, 09-json-settings-loader, 14-basic-expense-tracker

Acceptance Criteria

• 5 projects have browser-friendly versions
• Each version includes setup instructions for the chosen platform
• File I/O exercises use string input instead of file reads where necessary
• A README in the browser/ directory explains the approach

[travisjneuman]

Resolved in 36dceb1: Added 5 browser-based Pyodide exercises for Level 1 at projects/level-1/browser/ with CodeMirror editor and in-browser Python execution.