feat(core): expand interactive card schemas

[tejus3131]

Proposed Changes

Expands uagents_core.contrib.protocols.chat.cards payload validation to match predefined card schemas + element-tree primitives (parity w/ Agentverse card spec).

Predefined cards

• Carousel: style, root_cta, logo; image accepts URL | DisplayImage | list
• Detail: ExpandedChoice on sub-option choices; hero_image rich media; URL validation
• Form: cancel_cta; FormField shares InputFieldBase w/ custom-tree input
• Review: unchanged shape; stricter CtaAction validation

Shared

• DisplayImage (src, alt, aspect_ratio)
• CtaAction: non-empty selection required
• HTTP URL + aspect_ratio (W:H) validation on media fields

Custom element tree (card_kind: "custom")

• New: VideoNode
• ButtonNode: optional label (str | LabelWithIcon) or image; ≥1 required
• ButtonAction: selection | redirect, bypass_required_validation
• InputNode: full input kinds (date, time, multiselect, phone, etc.) + kind-specific validation
• ChoiceGridChoice.image: URL | DisplayImage
• GroupNode.gap: >= 1 when set
• Depth limit unchanged (MAX_ELEMENT_TREE_DEPTH = 8)

Metadata helpers (create_card_content, extract_card, etc.) unchanged — wire format still v1.

Follow-up to #897; single-file change in cards/__init__.py.

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Linked Issues

Closes #907

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Types of changes

• Bug fix (non-breaking change that fixes an issue).
• New feature added (non-breaking change that adds functionality).
• Breaking change (fix or feature that would cause existing functionality to stop working as expected).
• Documentation update.
• Something else (e.g., tests, scripts, example, deployment, infrastructure).

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Checklist

• I have read the CONTRIBUTING guide
• Checks and tests pass locally

If applicable

• I have added tests that prove my fix is effective or that my feature works
• I have added/updated the documentation (executed the script in python/scripts/generate_api_docs.py)

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Further comments

Validation tightened per spec (non-empty CTA selections, HTTP URLs, input kind rules). Valid payloads from #897 should still pass; loose/invalid payloads may now fail — intentional.

[Copilot]

Pull request overview

This PR expands the Pydantic validation models for interactive chat cards in uagents_core.contrib.protocols.chat.cards to align payload validation with the Agentverse interactive card specification, while keeping the metadata wire format at protocol version "1".

Changes:

• Added shared schema primitives and validators (e.g., DisplayImage, stricter CtaAction, HTTP URL + aspect_ratio validation).
• Expanded predefined card payload schemas (carousel/detail/form) and tightened validation rules for media and input field kinds.
• Extended custom element-tree support (e.g., VideoNode, richer ButtonAction, unified InputNode validation via InputFieldBase).

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