Update API spec with latest CMS changes

[rollki]

Update API spec with latest CMS changes + resolve merge conflicts

What changed

The previous commit (611ca77) was a large AI-assisted rewrite of vc.adoc to modernise the AsciiDoc format:

• Document header updated to proper AsciiDoc book format (:doctype: book, :toc: left, :toclevels: 3, :source-highlighter: highlight.js, :numbered:) — the TOC is now auto-generated, removing ~300 lines of manual link lists
• All section anchors simplified (e.g. [[_bad_request_error]] → [[bad-request]])
• Response tables reformatted from verbose 4-column to clean 3-column .Response Fields style
• Code block source types normalised to [source,http] and [source,json] (was [source,highlightjs,highlight,nowrap])
• Noise removed from HTTP examples (no more Content-Length, Content-Type headers in every block)
• New sections added: Proxy API, Association Info, Combined API (frontpage + watch-screen), Instructor API, Worlds API, Widgets / App Settings, GroupXClass, Promo

This commit

The rewrite left two unresolved git merge conflict markers committed into the file. This PR resolves them:

1. Conflict at the top — removed the stale 311-line manual TOC and the duplicate old-format "Method Not Allowed" section that was preserved from Updated upstream. The new format generates the TOC automatically, so this content was dead weight.
2. Conflict at the bottom — added the Archived Videos section from Stashed changes, documenting two new endpoints that exist in the codebase but were missing from the spec:

• GET /api/virtual-classes/v4.0/content-providers/{provider}/archived-videos — search, same parameters as Search Videos; returns items[].moderation_state: "archived"
• GET /api/virtual-classes/v4.0/content-providers/{provider}/archived-videos/{videoId} — details, same shape as Fetch Video; returns videoBrief.moderation_state: "archived" and videoDetails.hashId

⚠️ Needs review

The bulk of this spec was regenerated by Claude from the CMS codebase. Deep analysis flagged several areas that should be verified by a developer familiar with the API before this is shared externally:

• Response field names and nesting across all endpoints — particularly fields added recently (e.g. Worlds, Collections, Instructors)
• Example JSON payloads — values are illustrative and may not reflect real API output exactly
• Cross-references between sections (<>, <>) — anchor IDs were renamed and a wrong cross-reference would silently break the HTML render
• The Archived Videos section is new and has not been validated against a live environment