Split Ads how-to guides into per-platform guides

[MattiasBuelens]

Summary

Migrates the shared theoplayer/how-to-guides/01-ads/ guides into per-platform guides under how-to-guides/<platform>/ads/, following the existing cmcd pattern (shared MDX intro fragment + platform page). Only latest-version docs are touched; versioned docs are untouched.

Layout:

shared/ads/_<guide>-intro.mdx        # platform-independent intro (+ a few extra shared fragments for VMAP/dynamic scheduling/remarks)
web/ads/<guide>.mdx                  # "# <Title> on Web"  + <Intro /> + web-specific content
android/ads/<guide>.mdx
ios/ads/<guide>.mdx

Platform coverage was derived from the original guides' SDK tables/sections, so pages only exist where the feature exists. Final slugs (identical across platforms, so findMatchingTheoplayerDoc in src/util/platform.ts resolves the platform dropdown):

slug	web	android	ios
introduction	✔	✔	✔
set-up-vast-and-vmap	✔	✔	✔
yospace	✔	✔	✔
google-dai	✔	✔	✔
google-ima	✔	✔	✔
prebidjs	✔	✔	✔
subscribe-to-ad-events	✔	✔	✔
customizing-the-ad-overlay-text	✔	✔	✔
custom-ssai-integration	✔	✔	✔
mediatailor	✔	✔
block-detection	✔
visual-cues-for-mid-rolls	✔
freewheel	✔
spotx	✔

Slugs renamed while dropping the NN- prefixes:

old URL segment	new slug
how-to-set-up-vast-and-vmap	set-up-vast-and-vmap
how-to-subscribe-to-ad-events	subscribe-to-ad-events
how-to-display-visual-cues	visual-cues-for-mid-rolls

The Web and iOS custom-ssai-integration guides are new (written from the Android guide, adapted to player.ads.registerServerSideIntegration() on Web and registerServerSideIntegration(integrationId:integrationFactory:) + CustomServerSideAdInsertionConfiguration on iOS, with examples derived from the Yospace/Uplynk connectors).

Every old (numeric-stripped) URL, including /theoplayer/how-to-guides/ads/introduction/, gets a new redirectsTHEOPlayer.json entry pointing at the web page.

Notes:

• Shared fragments intentionally contain no intra-ads relative links (those would resolve against shared/ads/) and no platform-specific claims/links: DAI resources and IMA release-notes/compatibility links live in the per-platform pages, each linking only its own platform's references.
• All repo references to how-to-guides/01-ads/... were updated (knowledge base, FAQ, getting-started, UI/analytics/uplynk guides, changelog, pagination_next in how-to-guides/index.mdx).

Validated with npm run build (onBrokenLinks: 'throw', onBrokenAnchors: 'throw'), npm run check-format and npm run lint.

Link to Devin session: https://dolby.devinenterprise.com/sessions/463a67a9cb8c4e35994b9b111fb03a26
Requested by: @MattiasBuelens

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment, CI, and merge conflict monitoring