docs: Add box-style headers, section headers, feature markers, JSDoc, inline notes, footers

Added comprehensive documentation following project conventions:

Box-style headers (added/fixed where missing):
- All 17 files now have standard Project/Author/License headers

Section headers (// == == SECTION == ==):
- cache.helper.js: LRU CACHE CLASS, TTL CONFIGURATION, SINGLETON, EXPORTED HELPERS
- download.controller.js: DOWNLOAD LINKS HANDLER
- download.extractor.js: BASE64 DECODER, REDIRECT FOLLOWER, DOWNLOAD LINKS EXTRACTOR
- seasons.extractor.js: SEASONS EXTRACTOR
- watchOrder.extractor.js: WATCH ORDER EXTRACTOR
- extractPages.helper.js: PAGE EXTRACTOR
- pagination.helper.js: PAGINATION METADATA

Feature markers (// --- FEATURE: XYZ ---):
- cache.helper.js: LRU Cache, Per-Endpoint TTL, Cache Get/Set/Clear
- download.controller.js: Download Links
- download.extractor.js: Base64 Download Data Decoder, Redirect Chain Resolver, Download Links Extraction
- seasons.extractor.js: Season Information Extraction
- watchOrder.extractor.js: Watch Order / Related Anime Extraction
- streamResolver.extractor.js: Server Name Normalization, Stream URL Resolution, Batch Stream URL Resolution, M3U8 Quality Parser, Subtitle Track Extractor
- mirror.helper.js: Mirror Domain Configuration, Mirror Health Check, Working Mirror Discovery, Mirror Cache Reset, URL Builder, Resilient Fetch with Mirror Fallback, Mirror Status Reporter
- pagination.helper.js: Pagination Metadata Generator
- creatorInfo.js: Creator Attribution Object, Response Creator Injection Middleware

Function-level JSDoc (added/fixed):
- cache.helper.js: Full JSDoc on all 6 class methods (constructor, get, set, delete, clear, getStats, has) and 4 exported helpers

Inline notes for non-obvious logic:
- cache.helper.js: Lazy expiration, LRU re-insertion, singleton pattern
- download.extractor.js: HTML/JSON hybrid response handling, multiple selectors for different mirrors, redirect fallback
- random.extractor.js: maxRedirects, validateStatus, responseURL extraction
- schedule.extractor.js: Dual selector pattern for different mirror layouts
- animeInfo.extractor.js: Positional .bmeta selector fragility
- homeInfo.extractor.js: Dual selector for different layouts
- mirror.helper.js: 404 vs connection error handling
- animeInfo.controller.js: Accept both id and slug params

Footers (added where missing):
- cache.helper.js, download.controller.js, download.extractor.js, seasons.extractor.js, watchOrder.extractor.js, extractPages.helper.js, mirror.helper.js

All 68 source files now have complete documentation coverage (6/6 checks).

src/controllers/download.controller.js

@@ -18,6 +18,11 @@
 import { extractDownloadLinks } from "../extractors/download.extractor.js";
 import { getCache, setCache, TTL } from "../helper/cache.helper.js";
 
+// ══════════════════════════════════════════════════════════════
+// DOWNLOAD LINKS HANDLER
+// ══════════════════════════════════════════════════════════════
+
+// ---- FEATURE: Download Links ----
 /**
  * Handles GET /api/download requests. Returns download links
  * for the specified anime episode.
@@ -58,3 +63,4 @@ const getDownloadLinks = async (req, res, next) => {
 };
 
 export { getDownloadLinks };
+// ══════════════════════════════════════════════════════════════ END: download.controller.js