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.

packages/lint/src/rules/media.test.ts

@@ -348,7 +348,13 @@ describe("media rules", () => {
     expect(finding).toBeUndefined();
   });
 
-  it("flags <video> inside a sub-composition (media must be a host-root child)", async () => {
+  it("does not flag <video> inside a sub-composition (runtime drives nested media)", async () => {
+    // The runtime's global media sweep (querySelectorAll("video, audio")) drives
+    // media at any nesting depth, and startResolver re-bases each nested clip's
+    // local data-start by its host composition's absolute start. Sub-composition
+    // media is therefore seeked + decoded correctly in preview and render — see
+    // packages/core/src/runtime/{media,startResolver,init}.ts. A prior
+    // `media_in_subcomposition` rule wrongly hard-errored this and was removed.
     const html = `<template id="scene-template">
   <div id="root" data-composition-id="scene" data-width="1920" data-height="1080">
     <video id="v1" src="clip.mp4" data-start="0" data-duration="5" muted playsinline></video>
@@ -357,10 +363,7 @@ describe("media rules", () => {
 </template>`;
     const result = await lintHyperframeHtml(html, { isSubComposition: true });
     const finding = result.findings.find((f) => f.code === "media_in_subcomposition");
-    expect(finding).toBeDefined();
-    expect(finding?.severity).toBe("error");
-    expect(finding?.elementId).toBe("v1");
-    expect(finding?.message).toContain("sub-composition");
+    expect(finding).toBeUndefined();
   });
 
   it("does not flag media in a host-root (non-sub) composition", async () => {

packages/lint/src/rules/media.ts

@@ -396,29 +396,6 @@ export const mediaRules: Array<(ctx: LintContext) => HyperframeLintFinding[]> =
     return findings;
   },
 
-  // media_in_subcomposition — <video>/<audio> only render as a DIRECT child of the host
-  // root (index.html). Inside a sub-composition <template> the runtime never seeks/decodes
-  // them, so they render BLANK/black in preview and renders — and the other lint/validate
-  // passes otherwise miss it (only a per-frame snapshot reveals the blank panel).
-  ({ tags, options }) => {
-    const findings: HyperframeLintFinding[] = [];
-    if (!options.isSubComposition) return findings;
-    for (const tag of tags) {
-      if (tag.name !== "video" && tag.name !== "audio") continue;
-      const elementId = readAttr(tag.raw, "id") || undefined;
-      findings.push({
-        code: "media_in_subcomposition",
-        severity: "error",
-        message: `<${tag.name}${elementId ? ` id="${elementId}"` : ""}> is inside a sub-composition. The runtime only drives media that is a DIRECT child of the host root (index.html); media inside a sub-comp <template> is never seeked/decoded and renders BLANK/black in preview and renders.`,
-        elementId,
-        fixHint:
-          "Move the media OUT of the sub-composition: place the <video>/<audio> as a direct child of #root in index.html, positioned over the scene, and drive any per-scene motion on the MAIN timeline at global time (a sub-comp timeline cannot reach host elements). See composition-patterns.md archetype B.",
-        snippet: truncateSnippet(tag.raw),
-      });
-    }
-    return findings;
-  },
-
   // self_closing_media_tag
   ({ source }) => {
     const findings: HyperframeLintFinding[] = [];