Rewrite agent guidance and clean up comments

[colinds]

Summary

• keep the README focused on features, setup, tools, authentication, and configuration
• put the shared Forkable tool contract in one forkable skill
• make forkable-friday a small workflow extension and keep forkable-setup focused on setup
• document cross-platform browser import and expected credential prompts
• remove stale, decorative, and narrative comments while preserving security and wire-format invariants

The source, test, and smoke-test cleanup is behavior-neutral. An AST comparison confirmed that all 22
changed code files are identical after comments and location metadata are removed.

Verification

• all three bundled skills pass the skill validator
• bun run check (202 tests in the normal timezone and 202 in Asia/Kolkata)
• packaged smoke test with Bun and Node
• package contains forkable, forkable-friday, and forkable-setup

Stack: 4 of 4. Depends on #2.