Add mixed templates and bounded native carousels

[purpshell]

Linked Devices now build canonical native reply/CTA controls and hydrated templates for replies mixed with URL/call CTAs. Enforce ten total controls and at most three CTAs, preserve stable reply IDs/context, and reject unsupported reply/copy or reply/catalog mixtures. Add typed 2–10-card image/video carousel construction with homogeneous controls per card and unique reply IDs across cards.

Hydrated delivery uses empty root biz/hsm metadata without fabricated approval, category or verified attribution. Native flow retains its distinct category limits. Full Go tests pass at a2033af. Integrated Inspector evidence includes encrypted mixed direct/group controls and typed 2/10-card direct plus 2-card group carousels; the complete consumer matrix also passes all three media-header types and native campaign test-send/launch/reply attribution.

Backend consumer: https://github.com/polymorfa/polymorfa/pull/562. Draft only: no main merge, tag, publication or Meta/mobile availability claim. Repin consumers to the reviewed main revision before release.

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