feat: improve skills context efficiency

[skatesham]

Description

This PR improves the project skills structure to reduce unnecessary context usage while preserving the existing technical guidance.

The main changes are:

• Reduced large, single-file skills to smaller core SKILL.md files.
• Moved detailed technical documentation into focused references/ files.
• Kept only frequently needed rules and decision guidance in the main skill files.
• Added explicit reference routing so agents load additional context only when required by the current task.
• Removed model-specific wording such as Instructions for Claude in favor of model-agnostic instructions.
• Improved skill descriptions, operational rules, and validation steps where applicable.
• Preserved the original technical guidance while making it more efficient to consume.

For example, instead of loading extensive documentation about events, extensions, migration behavior, and debugging patterns for every task, the core skill now points to the relevant reference:

Problem	Read
Request does not fire	references/request-not-firing.md
Swap missing or wrong content	references/swap-problems.md
Extension or inheritance issue	references/extensions-and-inheritance.md

This should reduce unnecessary context usage and make the skills easier to maintain without changing htmx runtime behavior.

Corresponding issue: N/A

Testing

These changes affect skill/documentation organization only and do not modify htmx runtime source code.

I manually verified that:

• the core skill files retain the important behavioral rules;
• detailed guidance remains available through the corresponding references/ files;
• reference paths are valid and map to the appropriate topics;
• no relevant migration, debugging, or extension-authoring guidance was intentionally removed.

No runtime tests were added because this change does not affect executable htmx code.

Checklist

• I have read the contribution guidelines
• I have targeted this PR against the correct branch (master for website changes, dev for source changes)
• This is either a bugfix, a documentation update, or a new feature that has been explicitly approved via an issue
• I ran the test suite locally (npm run test) and verified that it succeeded