Add exhaustive codebase documentation

[Copilot]

Created comprehensive technical documentation covering the entire mvsep-cli codebase architecture, implementation, and operational details.

Changes

New file: CODEBASE_REPORT.md (~1,000 lines)

• Source code analysis: Detailed breakdown of all 5 core files (Program.cs, MOTM.cs, CliFetcher.cs, MvsepJson.cs, Utils.cs) including purpose, key components, methods, and design patterns
• Architecture documentation: Application flow diagrams, command structure, separation algorithms, and integration points
• Configuration reference: Project files (.csproj, .sln), build settings, launch profiles, and .NET 10 upgrade history
• Dependencies mapping: NuGet packages (System.CommandLine, Spectre.Console), external tools (ffmpeg), and MVSEP API endpoints
• Operational guide: Build instructions, usage examples for both single and batch modes, output file naming conventions
• Technical debt inventory: Known limitations, performance considerations, security notes, and maintenance recommendations
• Code metrics: Line counts, complexity analysis, and quality assessment

Excludes README.md per requirements.

Original prompt

Create an exhaustive report of the codebase. Ignore the README file.

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