fix(skills): stop embedded-captions shipping author-only paths; dedupe slideshow (#3225)

* fix(skills): stop embedded-captions shipping author-only paths

The skill is distributed via `hyperframes skills` (--copy, so the installed
bundle matches the published tree), but three shipped files pointed at
directories that only exist on the original author's machine.

- references/test-set.md: deleted. Nothing in the skill referenced it (zero
  inbound links across all 140 files), and its corpus lives at
  ~/Downloads/heygen_relevant_videos/, so it was neither reachable nor runnable.
- SKILL.md / dna/README.md: the retired 54-template archive was stated as
  living at a ~/Downloads path. Keeps the fact, drops the false location.
- themes/PORTING.md: marked maintainer-only. It authors new theme DNAs rather
  than using the skill, nothing links it, and its inputs (the cap_fx3 demos,
  the frame corpora, CONTRACT.md) are not distributed. The paths stay as the
  author's original layout, now explicitly labelled as names for the inputs.

The 10 references to ~/Downloads/hyperframes are untouched: those are the
documented last resort in a real chain (HYPERFRAMES_ROOT -> in-repo -> that
path), and every file carrying it also carries the env var.

Regenerates skills-manifest.json, which hashes the whole skill directory.

Closes #3219

— Rames Jusso (James's assistant)

* fix(skills): delete themes/PORTING.md instead of marking it internal

Nothing in the skill referenced it, its inputs are not distributed, and git
history keeps it recoverable. Marking a dead procedure still ships the dead
procedure.

— Rames Jusso (James's assistant)

* fix(skills): remove duplicated media-cleanup block in slideshow

The media-cleanup and global-nav-mute sections appeared twice in
skills/slideshow/SKILL.md. The two copies were not identical: the later one
was missing the paragraph requiring custom media controls to sync through
media events. Deletes the incomplete copy, keeps the complete one.

Originally authored in #3218. Carried here re-signed because the org requires
signed commits and both changes regenerate skills-manifest.json, which would
otherwise conflict between the two PRs.

Co-authored-by: Lance Curtis <69400491+imprimisxo@users.noreply.github.com>

* chore(skills): regenerate manifest for slideshow + embedded-captions

— Rames Jusso (James's assistant)

* chore(skills): record the two embedded-captions deletions in the guard

check-no-main-deletions.mjs deliberately has no blanket override, so each
intentional deletion is named with its reason and shows up in review.

— Rames Jusso (James's assistant)

---------

Co-authored-by: Lance Curtis <69400491+imprimisxo@users.noreply.github.com>

skills/embedded-captions/dna/README.md

@@ -13,8 +13,8 @@ shallow presets — every render is already fitted to its footage.
 
 Every classic DNA's **home is Cinematic (column)** — that is where all ten were
 built and validated. (Standard/rail mode was retired 2026-06-12; the verbatim-rail
-need is served by the `anchor` theme. The old rail combos live in
-`~/Downloads/embedded-captions-archive/`.)
+need is served by the `anchor` theme. The old rail combos are archived outside
+this repo and are not distributed with the skill.)
 
 ## The ten