wiki: add firewalld mail ports reset article + session updates

- New article: firewalld mail ports wiped after reload (IMAP + webmail outage)
- New article: Plex 4K codec compatibility (Apple TV)
- New article: mdadm RAID recovery after USB hub disconnect
- Updated yt-dlp article
- Updated all index files: SUMMARY.md, index.md, README.md, category indexes
- Article count: 41 → 42

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

03-opensource/media-creative/yt-dlp.md

@@ -40,19 +40,15 @@ yt-dlp -o "/path/to/output/%(title)s.%(ext)s" URL
 
 ## Plex-Optimized Download
 
-For Plex direct play, you want H.264 video in an MP4 container with embedded subtitles:
+Download best quality and auto-convert to HEVC for Apple TV direct play:
 
 ```bash
-yt-dlp -f 'bestvideo[ext=mp4]+bestaudio[ext=m4a]/bestvideo+bestaudio' \
-  --merge-output-format mp4 \
-  -o "/plex/plex/%(title)s.%(ext)s" \
-  --write-auto-subs --embed-subs \
-  URL
+yt-dlp URL
 ```
 
-- `-f 'bestvideo[ext=mp4]+bestaudio[ext=m4a]/...'` — prefer MP4 video + M4A audio; fall back to best available
-- `--merge-output-format mp4` — merge streams into MP4 container (requires ffmpeg)
-- `--write-auto-subs --embed-subs` — download auto-generated subtitles and bake them in
+That's it — if your config is set up correctly (see Config File section below). The config handles format selection, output path, subtitles, and automatic AV1/VP9 → HEVC conversion.
+
+> [!note] `bestvideo[ext=mp4]` caps at 1080p because YouTube only serves H.264 up to 1080p. Use `bestvideo+bestaudio` to get true 4K, then let the post-download hook convert AV1/VP9 to HEVC. See [Plex 4K Codec Compatibility](../../04-streaming/plex/plex-4k-codec-compatibility.md) for the full setup.
 
 ---
 
@@ -92,15 +88,17 @@ Persist your preferred flags so you don't repeat them every command:
 ```bash
 mkdir -p ~/.config/yt-dlp
 cat > ~/.config/yt-dlp/config << 'EOF'
--f bestvideo[ext=mp4]+bestaudio[ext=m4a]/bestvideo+bestaudio
+--remote-components ejs:github
+--format bestvideo+bestaudio
 --merge-output-format mp4
+--output /plex/plex/%(title)s.%(ext)s
 --write-auto-subs
 --embed-subs
---remote-components ejs:github
+--exec /usr/local/bin/yt-dlp-hevc-convert.sh {}
 EOF
 ```
 
-After this, a bare `yt-dlp URL` uses all your preferred settings automatically.
+After this, a bare `yt-dlp URL` downloads best quality, saves to `/plex/plex/`, embeds subtitles, and auto-converts AV1/VP9 to HEVC. See [Plex 4K Codec Compatibility](../../04-streaming/plex/plex-4k-codec-compatibility.md) for the conversion hook setup.
 
 ---