Epic: Claude Code Integration

[planger]

Based on the initial integration of Claude Code (see #16273), this epic contains a list of ideas of what can be done next:

• Providing Claude Code with much more power and insight into Theia, e.g. by hooking Theia up as an MCP server with Claude Code to read tasks, obtain diagnostics, control launches and debug sessions, etc.
• Support plan/edit modes: Here I'd suggest to introduce a generic mode concept in Theia AI and use it for Claude Code too. We could use the new chatInputReceivingAgent to determine the agent and ask it whether it provides modes. If yes, we could show them in the Chat UI for selecting (toggling through e.g. with Shift-Tab like in Claude Code)
• Switch welcome message based on addressed chat agent by listening to chatInputReceivingAgent context key
• Support for images
• Better task rendering based on the agent delegation UI we have in Theia AI
• Cancel spinner in Todo tool renderer, if the chat request is canceled
• Maybe there are a few more message types / tools that require custom rendering
• Some more preferences, like max-turns, allowed/disallowed tools
• Hooking up MCP support of Claude Code with the Theia MCP server registry
• Connecting Claude Code with the Agent History view (currently only tracked in Output channel)