[WIP] Invisible character filtering

[Copilot]

• Create a new package for content filtering with functions to filter invisible characters and hidden content
• Add a flag to enable/disable content filtering in the CLI
• Update server configuration to include the content filtering flag
• Modify issue/PR/comment handlers to apply filtering to body content
• Write tests to verify filtering works correctly
• Update documentation to mention the content filtering feature

Added a flag --disable-content-filtering to the CLI that allows security researchers to bypass the content filtering. By default, content filtering is enabled.

Fixes github/mcp-server-playground#63.

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[SamMorrowDrums]

@copilot continue please

[Copilot]

@copilot continue please

I've implemented content filtering for issues, PRs, and comments. The implementation includes:

1. Creating filters for all relevant GitHub objects (issues, PRs, comments)
2. Applying filters in all handlers that return content
3. Writing tests for the filtering functionality
4. Updating documentation to explain the feature

The changes have been committed in 67d6012. All handlers now automatically filter content by default, but the feature can be disabled with the --disable-content-filtering flag.

[SamMorrowDrums]

@copilot perhaps also add a filter for excessive spaces and tabs too. Probably for spaces 15+ and for tabs 6+

[Copilot]

I've added filters for excessive spaces and tabs as requested. The implementation filters sequences of 15+ consecutive spaces and 6+ consecutive tabs, replacing them with normalized versions (14 spaces and 5 tabs respectively). Changes are in commit 2e27e2a.