Improve researcher tool filter validation and error handling

Changes

• Enhanced filter validation: Added tracking of invalid filter fragments in the research filter system
• Better error reporting: The researcher tool now returns descriptive error messages when invalid filters are used, including suggestions for valid filters
• Optimized topic filtering: Improved query logic when filtering by topic IDs to avoid unnecessary complex queries
• Updated documentation: Fixed misleading text about reasoning feature scope (not just Sonnet 3.7)

Technical Details

• Added invalid_filters tracking in Filter class to collect unrecognized filter terms
• Modified process_filters method to accumulate invalid filters instead of returning filtered terms
• Enhanced researcher tool to check for invalid filters and return early with helpful error messages
• Fixed database queries by using simpler topic ID filtering when no other filters are applied (dont OR everything)
• Added comprehensive test coverage for invalid filter handling and topic-specific filtering

Benefits

• Users get immediate feedback when using incorrect filter syntax
• Reduced confusion with clearer error messages that include filter documentation
• More accurate feature documentation