feat(copilot): add openChainlitCopilot and closeChainlitCopilot functions

[hztBUAA]

Summary

Adds two new window functions for programmatic control of the copilot widget:

• window.openChainlitCopilot() - explicitly opens the copilot chat window
• window.closeChainlitCopilot() - explicitly closes the copilot chat window

These complement the existing window.toggleChainlitCopilot() function by allowing host pages to set a specific open/close state without needing to track the current state of the widget.

Motivation

As described in #2579, the toggle-only API is insufficient for common use cases like:

• Auto-opening the chat after a delay (e.g., setTimeout(() => window.openChainlitCopilot(), 5000)) without disturbing users who already opened it
• Closing the copilot in response to an external event without risking accidentally opening it
• Integrating with external UI components that have explicit open/close semantics

Changes

• libs/copilot/index.tsx: Added openChainlitCopilot and closeChainlitCopilot to the global Window interface type declarations
• libs/copilot/src/app.tsx: Added the same type declarations to the duplicate Window interface
• libs/copilot/src/widget.tsx: Implemented the two functions using setIsOpen(true) and setIsOpen(false), with proper cleanup on unmount (matching the existing pattern for toggleChainlitCopilot)

Test plan

• Mount the copilot widget and call window.openChainlitCopilot() from the browser console - copilot should open
• Call window.openChainlitCopilot() when already open - should remain open (no-op)
• Call window.closeChainlitCopilot() - copilot should close
• Call window.closeChainlitCopilot() when already closed - should remain closed (no-op)
• Call window.toggleChainlitCopilot() - should still work as before
• Unmount widget and call window.openChainlitCopilot() - should log error to console

Closes #2579

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Summary by cubic

Add window.openChainlitCopilot() and window.closeChainlitCopilot() to let host pages explicitly open or close the Copilot chat. This complements the existing toggle and enables safe auto-open/close flows without tracking state.

• New Features
  • Exposed openChainlitCopilot and closeChainlitCopilot on window; added type declarations in libs/copilot/index.tsx and libs/copilot/src/app.tsx.
  • Implemented in libs/copilot/src/widget.tsx via setIsOpen(true/false) with error logging when the widget is unmounted.

^{Written for commit 94a03a1. Summary will update on new commits.}

[cubic-dev-ai]

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