fix(create-expert): use appendTextFile instead of editTextFile

[FL4TLiN3]

Summary

Fix ecosystem-builder instruction to use the correct tool for appending content to files.

Problem

The instruction said:

Use editTextFile to APPEND the Expert ecosystem to the existing perstack.toml.

But per docs/making-experts/base-skill.md:

• editTextFile: "Performs search-and-replace in text files" (requires oldText)
• appendTextFile: "Appends content to existing files" (directly adds to end)

Solution

Changed to:

Use appendTextFile to add the Expert ecosystem to perstack.toml.

Test plan

• CI passes
• Generated experts use correct file operation

Closes #354

🤖 Generated with Claude Code

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Note

fix(create-expert): correct file-append instruction

• Updates ecosystem-builder instructions in create-expert-toml.ts to use appendTextFile (after reading the file) for adding experts to perstack.toml, replacing the incorrect editTextFile guidance and clarifying not to modify model/runtime/provider settings
• Adds a changeset (.changeset/use-append-text-file.md) for a patch release

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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