[MaartenRimaux]

Summary

Jira: ADS-590 — supersedes #891.

Customers could not see which ad workflows OptiView Ads supports, and the intro still said "VOD support coming soon". This PR adds a top-level Ad workflows section, organized by use case first and ad source second:

Ad workflows            overview: hybrid SGAI/SSAI, Live vs VOD, workflow matrix
├─ Live                 live channels: timebase, break creation, manifest polling
│  ├─ Static assets
│  ├─ Your ad server (VAST)
│  └─ Google Ad Manager  Pod Serving (SGAI) and DAI (SSAI)
└─ VOD                  VOD channels: mediatime, pre/mid/post-roll, pause ads, snapback
   ├─ Static assets
   ├─ Your ad server (VAST)
   └─ Google Ad Manager

• Each workflow page is self-contained: break example for that use case, app requirements, layouts, targeting, tracking and troubleshooting.
• The content that is identical for live and VOD comes from partials in ads/workflows/_shared/, so it has a single source.

Other changes:

• Intro: removes "VOD support coming soon" and describes the hybrid live + VOD platform, with a workflow table.
• Concepts: Channels gets a streamType section and the mediatime timebase. Breaks gets the mediatime start.
• SDK overview: the ad-source table now points to the new section, and mode is documented as following the channel's delivery rules by default.
• Carried over from Ads: split the SDK docs by ad workflow (static assets, VAST, Google Pod Serving) #891:
  • platform pages without the Google prerequisite
  • getting-started schedules a static asset
  • ad-tag-parameters covers VAST and the $OPTIVIEW_* macros
  • the SDK 1.0.0 corrections (gam is only an opt-out, the break's assetParameters win, ima3.js / ima3_dai.js requirements)
• The workflow pages from Ads: split the SDK docs by ad workflow (static assets, VAST, Google Pod Serving) #891 (player-integration/optiview-ads-sdk/ad-workflows/) are replaced by the pages above.

Test plan

• prettier --check and npm run lint pass
• All changed MDX files compile with @mdx-js/mdx
• Local link and anchor check on all Ads pages: no new problems
• CI build passes (onBrokenLinks / onBrokenAnchors: throw)
• Review the preview: the sidebar shows Ad workflows after Getting started, and the cards render on the overview

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