fix: Update skill documentation and improve resource handling instruc…

[Iamsdt]

This pull request updates how available skills and their usage instructions are presented to the user. It removes the resource listing from individual skill details and provides clearer, step-by-step instructions for using skills in the skill registry. The trigger table is now more readable and informative, especially about when and how to use each skill.

Skill usage instructions and presentation improvements:

• The skill registry (build_trigger_table in registry.py) now includes a step-by-step "How to Use Skills" section, making it clearer how to load and use skills and their resources.
• The trigger table format has been changed from a markdown table to a list format, showing each skill with its triggers (up to four, with a count if more exist), improving readability and context.

Resource listing changes:

• The resource listing and instructions for loading resources have been removed from the individual skill detail output in set_skill, streamlining the skill content.

[codecov]

Codecov Report

❌ Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
agentflow/skills/registry.py	77.77%	1 Missing and 1 partial ⚠️

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