refactor: remove legacy foundation components

[kettasoft]

Summary

Remove the unused resource-bag layer and legacy filtering helpers that no longer participate in Filterable's execution pipeline.

What changed

• removed Resources, FilterableSettings, and all specialized resource bags
• removed the obsolete getResources() and settings() APIs from Filterable and its facade PHPDoc
• stopped synchronizing allowed fields and relations into duplicate bag state
• removed legacy field validators, mappers, relation parsers, and tree resolvers superseded by PayloadFactory and PayloadApplier
• updated the API documentation and changelog to reflect the streamlined foundation

Why

These components were remnants of an older architecture. They duplicated state already owned by Filterable, were not used by the current payload pipeline, and increased the amount of code initialized and maintained without affecting filtering behavior.

The active engines continue to read fields, relations, operators, sanitizers, and mappings from their canonical APIs and runtime context.