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>

build/icon.svg

@@ -1,12 +1,26 @@
 <svg width="256" height="256" viewBox="0 0 256 256" xmlns="http://www.w3.org/2000/svg">
-  <!-- Placeholder app icon (audit M3). Mirrors the in-app brand mark in
-       Onboarding.tsx: a white download arrow on a rounded square in the default
-       "teal" accent (theme.ts teal[80] = colorBrandBackground in light mode).
-       Replace with a designed asset before v1.0; regenerate icon.ico from this. -->
-  <rect x="0" y="0" width="256" height="256" rx="52" ry="52" fill="#148185"/>
-  <g fill="#ffffff">
-    <rect x="112" y="46" width="32" height="88" rx="12" ry="12"/>
-    <polygon points="82,114 174,114 128,176"/>
-    <rect x="66" y="190" width="124" height="20" rx="10" ry="10"/>
+  <!-- AeroFetch app icon (audit W14). A white download glyph — shaft + chevron over
+       a landing shelf — on the teal brand square, with a top-lit vertical gradient
+       drawn from the teal accent ramp (theme.ts teal 50→90, centred on teal[80]
+       #148185, the light-mode colorBrandBackground) and a soft upper sheen for depth.
+       The bold rounded strokes stay legible down to 16px. Regenerate the multi-size
+       .ico after any edit:
+         magick -background none build/icon.svg -define icon:auto-resize=256,128,64,48,32,16 build/icon.ico -->
+  <defs>
+    <linearGradient id="bg" x1="0" y1="0" x2="0" y2="1">
+      <stop offset="0" stop-color="#1aa6ab"/>
+      <stop offset="1" stop-color="#0d595c"/>
+    </linearGradient>
+    <linearGradient id="sheen" x1="0" y1="0" x2="0" y2="1">
+      <stop offset="0" stop-color="#ffffff" stop-opacity="0.16"/>
+      <stop offset="0.45" stop-color="#ffffff" stop-opacity="0"/>
+    </linearGradient>
+  </defs>
+  <rect x="0" y="0" width="256" height="256" rx="56" ry="56" fill="url(#bg)"/>
+  <rect x="0" y="0" width="256" height="256" rx="56" ry="56" fill="url(#sheen)"/>
+  <g fill="none" stroke="#ffffff" stroke-linecap="round" stroke-linejoin="round">
+    <path d="M128 56 L128 150" stroke-width="30"/>
+    <path d="M84 116 L128 160 L172 116" stroke-width="30"/>
+    <path d="M80 200 L176 200" stroke-width="26"/>
   </g>
 </svg>