Convert the scanner's plist parser and Node-style file shim to TypeScript and add small unit tests so common parser and file-reader failures are caught before we need to lean on Playwright or the higher-level scanner test.
Constraint: Must preserve current scanner behavior while tightening the lowest-level helper surface
Rejected: Jump straight to Mach-O parser conversion | harder to isolate regressions without first proving the smaller helper-test pattern
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Add small module-level regression tests for repeatable scanner breakage before expanding browser coverage
Tested: pnpm run typecheck; pnpm exec vitest run test/scanner/plist.test.ts test/scanner/file-api.test.ts test/scanner/client.test.ts; pnpm run test; pnpm run test:browser
Not-tested: Production deploy behavior prior to push
