Prevent Silent File Clobbering: Add Overwrite Flag & Existence Check for Output Files

[joshuayoes]

🧐 What & Why

screenshot and record_video overwrite existing files without warning, risking data loss.
An explicit opt-in to overwrite makes destructive actions deliberate.

🛠️ Proposal

1. Before writing, execute fs.existsSync(absolutePath).
2. If the file exists and force/overwrite flag is not supplied, throw:

   File already exists. Re-run with --overwrite to replace it.
   

3. Add a force?: boolean parameter (default false) to screenshot, mirroring the flag already available on record_video.
4. Thread this flag into command-line args (--force) where needed.

✅ Acceptance Criteria

• Existing files are only overwritten when --overwrite (or JSON arg force: true) is passed.
• Unit tests: overwrite denied vs. allowed.
• README / CLI help updated with new flag.

⚠️ Backward Compatibility

Scripts relying on implicit overwrites must now pass --overwrite explicitly.