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/reveal.ts

@@ -13,11 +13,29 @@ import { extname, isAbsolute } from 'path'
  */
 const OPENABLE_EXTENSIONS = new Set([
   // video
-  '.mp4', '.mkv', '.webm', '.mov', '.avi', '.flv', '.ts', '.m4v', '.3gp', '.ogv',
+  '.mp4',
+  '.mkv',
+  '.webm',
+  '.mov',
+  '.avi',
+  '.flv',
+  '.ts',
+  '.m4v',
+  '.3gp',
+  '.ogv',
   // audio
-  '.mp3', '.m4a', '.opus', '.ogg', '.oga', '.aac', '.flac', '.wav', '.wma',
+  '.mp3',
+  '.m4a',
+  '.opus',
+  '.ogg',
+  '.oga',
+  '.aac',
+  '.flac',
+  '.wav',
+  '.wma',
   // subtitle sidecars (plain text — safe to open)
-  '.vtt', '.srt'
+  '.vtt',
+  '.srt'
 ])
 
 /** Open a downloaded media file with its default app. Returns '' on success,