Expand Developer Guide and File Reference with missing content
Developer-Guide.md: add Adding a New Setting, Adding a New Menu Item,
Adding a New Dialog, Adding a New Script Source Type, and Filter and Sort
System sections
File-Reference.md: add missing functions (Tabs_ApplyFilter/Sort/Match,
Window_ShowTrayMenu/ApplyThemeToChildren/OpenExeFolder, App_BuildAppDataPath);
add ScriptMeta, SyncResult, ExtraRepo, LocalDir, SortMode/ThemeMode to Key
Structs; split Constants into limits + layout tables with missing entries;
add Timer IDs; expand Colour System with COL_INFO_ZONE and fixed-colour
constants; fix AppState (add active_folder_name) and Settings (add qbar_target_exe)
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>