fix: correct skilz visit marketplace URL format

[RichardHightower]

This PR fixes the skilz visit command to generate correct marketplace URLs.

Problem

The visit command was generating incorrect marketplace URLs:

• Wrong base path: skillzwave.ai/skill instead of skillzwave.ai/agent-skill
• Wrong slug format: skill__SKILL suffix instead of clean owner__repo__skill format

Example

Before:
URL: https://skillzwave.ai/agent-skill/spillwavesolutions__sdd__sdd/

After:
URL: https://skillzwave.ai/agent-skill/spillwavesolutions__sdd__sdd/

Changes Made

URL Format Updates

• Base URL: https://skillzwave.ai/skill → https://skillzwave.ai/agent-skill
• Slug format: owner__repo__skill__SKILL → owner__repo__skill
• Single names: Assume spillwavesolutions organization for single skill names

Code Changes

• src/skilz/commands/visit_cmd.py: Updated resolve_marketplace_url() function
• tests/test_visit_cmd.py: Updated test expectations to match new URL format

Supported Formats

The command now correctly handles:

• skilz visit owner/repo/skill → owner__repo__skill
• skilz visit owner/repo → owner__repo__repo (skill = repo name)
• skilz visit skill → spillwavesolutions__skill__skill

Testing

• All 40 visit command tests pass
• Manual verification of URL generation
• Backward compatibility maintained for existing functionality

Impact

Users can now successfully visit correct marketplace pages using skilz visit command.