Release v1.4.20 with comprehensive audit fixes (140 issues) and expanded test coverage

- Speed calculation: raised minimum elapsed floor to 0.5s preventing unrealistic spikes
- Reconnect: exponential backoff with consecutive counter, clock regression protection
- Download engine: retry byte tracking (itemContributedBytes), mkdir before createWriteStream, content-length validation
- Fire-and-forget promises: all void promises now have .catch() error handlers
- Session recovery: normalize stale active statuses to queued on crash recovery, clear speedBps
- Storage: config backup (.bak) before overwrite, EXDEV cross-device rename fallback with type guard
- IPC security: input validation on all string/array IPC handlers, CSP headers in production
- Main process: clipboard memory limit (50KB), installer timing increased to 800ms
- Debrid: attribute-order-independent meta tag regex for Rapidgator filename extraction
- Constants: named constants for magic numbers (MAX_MANIFEST_FILE_BYTES, MAX_LINK_ARTIFACT_BYTES, etc.)
- Extractor/integrity: use shared constants, document password visibility and TOCTOU limitations
- Tests: 103 tests total (55 new), covering utils, storage, integrity, cleanup, extractor, debrid, update

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main/cleanup.ts

@@ -1,6 +1,6 @@
 import fs from "node:fs";
 import path from "node:path";
-import { ARCHIVE_TEMP_EXTENSIONS, LINK_ARTIFACT_EXTENSIONS, RAR_SPLIT_RE, SAMPLE_DIR_NAMES, SAMPLE_TOKEN_RE, SAMPLE_VIDEO_EXTENSIONS } from "./constants";
+import { ARCHIVE_TEMP_EXTENSIONS, LINK_ARTIFACT_EXTENSIONS, MAX_LINK_ARTIFACT_BYTES, RAR_SPLIT_RE, SAMPLE_DIR_NAMES, SAMPLE_TOKEN_RE, SAMPLE_VIDEO_EXTENSIONS } from "./constants";
 
 async function yieldToLoop(): Promise<void> {
   await new Promise<void>((resolve) => {
@@ -111,7 +111,7 @@ export function removeDownloadLinkArtifacts(extractDir: string): number {
         if (/[._\- ](links?|downloads?|urls?|dlc)([._\- ]|$)/i.test(name)) {
           try {
             const stat = fs.statSync(full);
-            if (stat.size <= 256 * 1024) {
+            if (stat.size <= MAX_LINK_ARTIFACT_BYTES) {
               const text = fs.readFileSync(full, "utf8");
               shouldDelete = /https?:\/\//i.test(text);
             }