fix(lint): drop false media_in_subcomposition rule (#2765)

The media_in_subcomposition rule blanket-errored every <video>/<audio>
inside a sub-composition, claiming nested media is "never seeked/decoded
and renders blank/black". This is false: the runtime discovers media with
a flat document.querySelectorAll("video, audio"), resolves each element's
host composition via closest("[data-composition-id]"), and rebases its
local data-start by the accumulated absolute start of every ancestor
composition (packages/core/src/runtime/{media,startResolver}.ts). Media
seeks and decodes at any nesting depth, verified end to end through the
producer render path.

- Remove the rule and flip its test to assert nested media is NOT flagged.
- Drop the now-dead media_in_subcomposition clause from the registry
  components test.
- Drop the equivalent pre-render guard from the faceless-explainer and
  pr-to-video assemble scripts.
- Correct the reference docs (hyperframes-core SKILL, data-attributes,
  variables-and-media, composition-patterns; hyperframes-cli
  lint-validate-inspect): media works at any depth. Preserve the one real
  constraint, that a sub-comp timeline cannot reach host-root elements, so
  host-root media motion is authored on the main timeline.

skills/hyperframes-core/SKILL.md

@@ -60,7 +60,7 @@ Surfaced here; full rationale in the linked reference. Do not violate:
 - No render-time clocks / unseeded `Math.random` / network / input-state; no `repeat: -1` (use a finite count). → `determinism-rules.md`
 - Animate only the visual-property allowlist; never tween `display` or raw `visibility`. GSAP `autoAlpha` and zero-duration timeline boundary sets are the only visibility exceptions, and only on non-clip elements or wrappers inside a clip. The framework alone controls `.clip` visibility. Do not `gsap.set` later-scene clips at page load. → `determinism-rules.md`
 - No `<br>` in body text; transformed elements must be block-level + sized; pulsing absolute decoratives need peak clearance. → `determinism-rules.md`
-- `<video>`/`<audio>` must be a **direct child of the host root** (never inside a sub-comp `<template>`/wrapper); the framework owns playback. → `variables-and-media.md`
+- `<video>`/`<audio>` work at **any nesting depth** (including inside a sub-comp `<template>` or wrapper); the framework owns playback and seeks/decodes media wherever it lives. The one caveat is timelines, not placement: a sub-comp timeline can't animate host-root elements. → `variables-and-media.md`
 - Every `id` must be unique across the **assembled** page; inside a sub-comp, prefix ids with the composition id (`#<id>-hero`). Duplicate `<video>`/`<img>` ids render **blank** — the producer injects frames by `getElementById`, and cross-file dupes slip past `lint`. → `composition-patterns.md`
 - A full-screen scene fill goes on a full-bleed **child** (`position:absolute; inset:0`), never on the composition root itself — the producer's frame compositing can drop the root element's own `background` (the frame renders **black**) even though preview/`snapshot` show it correctly. → `composition-patterns.md`