Add web-based report visualizer tool

[mohithshuka]

• Implements HTML/CSS/JS visualization tool for -out=report output
• Parses report.txt and displays subtitle pages as cards
• Shows timestamps, types, and subtitle activity
• Includes Chart.js timeline visualization
• Resolves [Proposal]:Web-Based Visualization for -out=report Output #1689

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{pull request content here}

[mohithshuka]

This PR implements the web-based visualization tool as proposed in #1689.
What's included:

• index.html: Main interface with file upload functionality
• styles.css: Modern, responsive design with gradient background
• script.js: Parser for report.txt files with visualization logic
• README.md: Documentation on usage and features

##How it works:

1. User uploads a report.txt file generated by ccextractor -out=report
2. JavaScript parses the file to extract subtitle pages, types, and timestamps
3. Each page is displayed as a card showing key information
4. A Chart.js bar chart visualizes subtitle activity across all pages

Features:

Fully client-side - no server required
Works by simply opening index.html in any browser
Responsive design for mobile and desktop
Visual timeline/graph of subtitle occurrences
Clean, modern UI

Testing:

The tool can be tested by:

1. Running CCExtractor with -out=report on any video file
2. Opening tools/report-visualizer/index.html in a browser
3. Uploading the generated report.txt file

Future enhancements (optional):

• GitHub Pages hosting for live demo
• Export functionality for filtered data
• More detailed timeline views with time-based graphs

[cfsmp3]

Closing this PR due to issues:

1. No changelog entry: The checkbox for changelog is unchecked, and new features should be documented.

2. Duplicate submission: This same report visualizer code appears in PR Feature/document timestamp map #2071 as well - please don't submit the same code in multiple PRs.

3. Not a core feature: While visualization tools can be useful, adding third-party dependencies (Chart.js CDN) and web tools to the repository requires discussion first. Consider hosting this as a separate project or discussing in an issue before submitting.

If you'd like to contribute tools like this, please open an issue first to discuss whether it fits the project scope.