feat(cas): add fullscreen mode support

[scottcmg]

What

Adds a mode?: "embedded" | "fullscreen" prop to the conversational-agent-chat widget. Previously the widget hardcoded Apollo's AutopilotChatMode.Embedded, so it could never render the standalone fullscreen experience — which is the default of the iframe-based chat this widget is meant to replace.

In fullscreen mode Apollo renders the agent sparkle icon next to the title (it gates that logo on chatMode === FullScreen), so this also resolves the "missing icon" gap vs. the existing standalone chat.

Changes

• types.ts — new public mode prop, defaults to "embedded" (non-breaking).
• ConversationalAgentChat.tsx — map mode to the Apollo enum in the chat config, add it to initChat deps so a prop change reinitializes, and apply a --fullscreen wrapper modifier class.
• ConversationalAgentChat.scss — --fullscreen drops the wrapper border so Apollo's own viewport-height container owns the chrome (avoids a double frame).
• stories — mode control + a dedicated Fullscreen story with a full-viewport decorator.
• tests — embedded default has no modifier class; fullscreen instantiates with mode: FullScreen and applies the class.

Notes

• Default stays "embedded" (non-breaking). The iframe app being replaced defaults to fullscreen — easy to flip if we want parity.
• Fullscreen expects the host to provide a full-viewport container (the Story models this).

Verification

• tsc --noEmit: clean
• tests: 87 passed in the package suite
• lint + i18n + prettier (pre-commit): clean

🤖 Generated with Claude Code

[github-actions]

📊 Coverage Report

Package	Line Coverage
datatable	88.29%
multi-file-upload	87.27%
conversational-agent-chat	89.07%
validation-station	87.75%