feat(yt-dlp): add wrapper with embedding + SponsorBlock defaults

Add functions/yt-dlp.fish, shadowing yt-dlp to prepend sane defaults
(--sponsorblock-remove all, --embed-subs, --embed-metadata,
--embed-thumbnail). Each default is suppressed when the user already
passes that flag, its alias (--add-metadata), its negation
(--no-embed-thumbnail), the --opt=value form (--sponsorblock-remove=...),
or the global --no-sponsorblock kill. User args pass through last so an
explicit flag wins on precedence. Gated as a C1 opinionated alias;
falls back to bare `command yt-dlp` when disabled.

Register yt-dlp as a recommended (rec tier) dependency in the fish-deps
catalog and document the function (§5.13) and dependency in the SSOT
and index.

docs/fish-config.index

@@ -151,6 +151,7 @@ superpowers=### superpowers
 media=## 5.13 Media and Utilities
 dng2avif=### dng2avif
 spark=### spark
+yt-dlp=### yt-dlp
 miscfns=## 5.14 Miscellaneous
 config-help=### config-help
 config-update=### config-update