refactor(scanner): type plist and file-api helpers

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

test/scanner/file-api.test.ts

@@ -0,0 +1,72 @@
+import { Buffer } from 'buffer'
+
+import {
+    describe,
+    expect,
+    it
+} from 'vitest'
+
+import {
+    File,
+    FileReader,
+    type FileReaderLoadEvent
+} from '~/helpers/scanner/file-api'
+
+describe( 'scanner file api shim', () => {
+    it( 'constructs a file from a buffer payload', () => {
+        const file = new File({
+            buffer: Buffer.from( 'hello world', 'utf8' ),
+            name: 'hello.txt',
+            type: 'text/plain'
+        })
+
+        expect( file.name ).toBe( 'hello.txt' )
+        expect( file.type ).toBe( 'text/plain' )
+        expect( file.size ).toBe( 11 )
+    } )
+
+    it( 'reads text content through the node FileReader shim', async () => {
+        const file = new File({
+            buffer: Buffer.from( 'scanner-text', 'utf8' ),
+            name: 'scanner.txt',
+            type: 'text/plain'
+        })
+        const reader = new FileReader()
+
+        const loadedText = await new Promise<string>( ( resolve, reject ) => {
+            reader.onerror = reject
+            reader.onload = event => {
+                const loadEvent = event as FileReaderLoadEvent
+
+                resolve( String( loadEvent.target.result ) )
+            }
+
+            reader.readAsText( file )
+        } )
+
+        expect( loadedText ).toBe( 'scanner-text' )
+    } )
+
+    it( 'reads binary content through the node FileReader shim', async () => {
+        const file = new File({
+            buffer: Buffer.from( [ 0xde, 0xad, 0xbe, 0xef ] ),
+            name: 'scanner.bin',
+            type: 'application/octet-stream'
+        })
+        const reader = new FileReader()
+
+        const loadedBuffer = await new Promise<Buffer>( ( resolve, reject ) => {
+            reader.onerror = reject
+            reader.onload = event => {
+                const loadEvent = event as FileReaderLoadEvent
+
+                resolve( loadEvent.target.nodeBufferResult )
+            }
+
+            reader.readAsArrayBuffer( file )
+        } )
+
+        expect( Buffer.isBuffer( loadedBuffer ) ).toBe( true )
+        expect( loadedBuffer.toString( 'hex' ) ).toBe( 'deadbeef' )
+    } )
+} )