Shrink the skill catalog and recover from more tool-call mistakes

Summary

• The skill catalog lists a skill once when several skills folders hold a copy with the same name and description.
• Skill descriptions in the catalog default to their first 200 characters instead of 1,024. A configured skill_description_bytes still sets a byte limit.
• The runtime notes for permission modes, noninteractive runs, verifying changed files, folder AGENTS.md rules, and MCP servers are shorter.
• shell accepts a call that sends an empty string or false for fields its action does not use.
• shell accepts a shell field that names the login shell on a run without a terminal.
• subagent wait accepts an agent field and ignores it.
• When edit_file cannot find old_string, the error shows the file lines it most likely meant.
• When old_string matches more than once, the error shows each match with the two lines before it.
• The TUI status line shows the first line of a multi-line file-tool failure.

Docs: vercel-labs/fx-web#256