fix(vscode): keep Flyde imports working after file moves

[nam157]

Fixes #112

/claim #112

Proposed Changes

• Register a VS Code onDidRenameFiles listener for Flyde flows.
• Rewrite relative source: file imports inside a moved .flyde flow so its existing imports still point to the same files after the move.
• Rewrite workspace .flyde files that reference a moved import target so importer flows keep resolving the target from its new location.
• Keep the path-rewrite logic in a small pure helper with focused regression coverage.

Proof

pnpm --filter @flyde/editor build
pnpm --filter @flyde/nodes build
pnpm --filter @flyde/loader build
pnpm --filter flyde-vscode compile
pnpm --filter flyde-vscode compile-tests
./vscode/node_modules/.bin/mocha --ui tdd vscode/out/test/flydeImportPathRewriter.test.js
pnpm --filter flyde-vscode lint

Results:

• flyde-vscode compile passed.
• flyde-vscode compile-tests passed.
• Focused Mocha suite passed: 4 passing.
• flyde-vscode lint passed with 0 errors; existing unrelated warnings remain in open-flyde-panel.ts, scan-importable-nodes.ts, and find-package-root.ts.

Checklist

• PR created against main.
• TypeScript compile passed.
• Regression tests added for moved flow imports and moved target references.
• No user-facing docs needed for this bug fix.