Harden audit findings: correctness, type-safety, Windows conventions & polish

Audit-pass over CODE-AUDIT.md (~48 items closed this pass; all verified —
typecheck + 234 tests + eslint + prettier green).

Correctness / bugs:
- B3: match the release checksum to the asset's filename line (no wrong-hash verify)
- B4: newline-safe metadata probe (one --print with a unit-separator delimiter)
- B5 / L88: guard the meta event against canceled items; progress no longer promotes
  a queued item outside pump()
- B7: cookie-login promise always resolves (handles destroy-without-close)
- L146: trim parser rejects >2 colon-group times; M36: Library selection counts only
  actionable rows
- L11 / L50 / L156 / L57 / L159 / L15 / L3: live queue count, empty-cookie message,
  schedule picker min, dead-code/comment cleanup

Type safety:
- Enable noUncheckedIndexedAccess + noFallthroughCasesInSwitch (15 real edge cases fixed)

Resilience / Windows / metadata:
- R5: settings write failure handled (no unhandled IPC rejection; reconciles to truth)
- W1 / W5 / W6: min window size, seeded folder picker, parented sign-in window;
  L147 dead macOS branches removed
- CL1: shared stdout markers; package/builder metadata (license, homepage, repository,
  copyright, tsbuildinfo glob)

Copy / docs / tests:
- M37 / SR9 dev-jargon cleanup in hints; M8 / M25 / M26 / L66 / L80 / L81 reconciled
- New unit tests for L35 (isValidMediaItem) and L36 (compareVersions)

This commit also checkpoints the previously-uncommitted feat/tray-background-clipboard
work it builds on: background running + auto-download, library clipboard detection,
tray, binary management & library scale, credential encryption at rest, the shared
jsonStore and ui/ primitives, and the eslint/prettier tooling.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/schedule.ts

@@ -21,10 +21,15 @@ function schtasks(args: string[]): Promise<{ code: number; stdout: string; stder
   return new Promise((resolve) => {
     // Resolve schtasks from System32 by absolute path, not the bare name, so a
     // planted schtasks.exe on PATH / in the CWD can't be invoked instead. (audit F3)
-    execFile(getSystem32Path('schtasks.exe'), args, { windowsHide: true }, (err, stdout, stderr) => {
-      const code = err ? ((err as { code?: number }).code ?? 1) : 0
-      resolve({ code, stdout: String(stdout), stderr: String(stderr) })
-    })
+    execFile(
+      getSystem32Path('schtasks.exe'),
+      args,
+      { windowsHide: true },
+      (err, stdout, stderr) => {
+        const code = err ? ((err as { code?: number }).code ?? 1) : 0
+        resolve({ code, stdout: String(stdout), stderr: String(stderr) })
+      }
+    )
   })
 }