fix(typefully): improve invalid API key UX

[linuz90]

TL;DR

Broken or expired Typefully API keys now produce a clear authentication failure instead of a generic HTTP 401 or a softened setup warning. The skill instructions also tell agents to stop and ask the user to refresh setup, rather than falling back to browser, web UI, or localhost access.

Root Cause

The CLI only had hard-stop handling for missing API keys. Invalid keys came back as generic 401 API errors, and setup/default-social-set paths wrapped those errors as softer fetch/access failures, leaving agents room to improvise another access path.

Summary

• Fix 401 auth handling by adding a shared authentication failure message and details for Typefully API 401 responses.
• Fix setup and default social set flows so invalid keys also hard-stop with setup guidance instead of being wrapped as generic fetch/access failures.
• Update agent-facing docs and changelog to cover missing, invalid, and expired keys, and explicitly forbid web UI/browser/localhost fallback for draft access.
• Clarify X Article Markdown review guidance so agents do not flag Typefully-normalized bold/link Markdown as broken when the rendered article is correct.
• Clean up dated changelog sections so shipped Typefully skill entries use plain date headings instead of Unreleased or bracketed dates.
• Add regression coverage for direct API calls, setup default validation, setup social-set discovery, and default social set configuration.

Validation

• git diff --check
• npm run test:common
• npm run test:config
• npm test

After Merge

• Users with an installed copy of the Typefully skill should update it through their normal skills.sh / Claude plugin flow to receive the new behavior.