Improve documentation for feature enable/disable filters

[huzaifaalmesbah]

Description

The ai_feature_{$feature_id}_enabled filter is documented in the DEVELOPER_GUIDE.md, but the documentation could be improved to better explain:

1. Where the filter is actually defined in the codebase
2. How it works internally (the flow from Feature_Loader to Abstract_Feature)
3. More practical use cases with clear examples
4. When and why developers would use this filter

Current Documentation

The current documentation shows usage examples but doesn't explain the implementation or provide enough context about when to use it.

Proposed Improvements

• Add a "How It Works" section explaining the internal flow
• Add a code reference showing where the filter is applied
• Include more real-world use case examples
• Add a diagram or flowchart showing the feature initialization process

Affected Files

• docs/DEVELOPER_GUIDE.md

Impact

This will help developers better understand the plugin's feature system and how to customize it.

[jeffpaul]

I'd like to wait for #51 and #61 to get merged in as there are still some architectural discussions being had there that could update what's called out in the issue and respective PR in #69.

[huzaifaalmesbah]

Thanks, @jeffpaul — sounds good.

[jeffpaul]

@huzaifaalmesbah the PRs that needed to get merged have done so, mind reviewing #69 to see what updates should be informed by code now in trunk?