Fix local Flyde imports after file moves

[ajjucoder]

Summary

• Rewrites relative .flyde file imports inside a moved flow so they still point at the same targets from the new folder
• Updates other workspace .flyde files that reference a moved .flyde target
• Adds focused regression coverage for both path rewrite cases

/claim #112

Verification

• npx -y pnpm@10.12.4 install --ignore-scripts
• npx -y pnpm@10.12.4 --filter @flyde/core --filter @flyde/loader --filter @flyde/nodes --filter @flyde/editor build
• npx -y pnpm@10.12.4 --filter flyde-vscode compile
• npx -y pnpm@10.12.4 --filter flyde-vscode compile-tests
• npx -y pnpm@10.12.4 --filter flyde-vscode exec mocha --ui tdd out/test/flydeImportPathRewriter.test.js
• npx -y pnpm@10.12.4 --filter flyde-vscode lint (passes with 4 existing warnings in unrelated files)
• git diff --check