fix: skillnet-ai 0.1.x compatibility (JSON output, download layout, analyze flags)

[fatihmert]

Summary

skillnet-ai 0.1.x changed the CLI in ways that break several tools. This PR adapts the server to 0.1.2:

• Search and download: results are read from --json ({ok, data, error}) instead of regex-scraping the rich table. CLI errors now come back with their message and hint (e.g. Destination exists; use --overwrite).
• import_best_skill / get_skill_rules: the CLI writes a skill to <target>/<skill-name>/, so both tools listed the target directory, found no SKILL.md, and answered "No .md documentation found". They now use the path the download reports, and existing caches are resolved the same way.
• analyze_skills: --save/--no-save were removed in 0.1.x, so the tool now takes output_dir and force.
• download_skill: new overwrite option. The token is now handed over as GITHUB_TOKEN instead of -t <token>, which keeps it out of the process list (the CLI's own help recommends this).
• health_check: uses skillnet doctor --json and reports the CLI version. A new SKILLNET_BIN variable points at a CLI outside PATH, e.g. a uv tool install.
• Version 1.4.0. The lockfile's stale root metadata (1.0.0/ISC) now matches package.json.

Testing

• npm test: 19 passed. New tests cover JSON parsing, result formatting and skill-folder resolution. Command-builder expectations are updated.
• Stdio smoke test against the real CLI (skillnet-ai 0.1.2):
  • health_check and search_skills succeed.
  • import_best_skill and get_skill_rules with topic pdf download to .temp_skills/pdf/summarize/SKILL.md and return its content. Before this change they returned "No .md documentation found".
• Known upstream issue, not fixed here: for some topics the top-ranked skill lives in a repository that has since moved. The CLI does not follow GitHub's 301 and fails with GitHub API Error [301]. The tool now reports that error cleanly.

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