[FEATURE] Plugin API for interactive TUI elements (clickable overlays, panels, keybinding actions)

Plugins can add skills, commands, hooks, agents, MCP servers and a statusline, but nothing that renders or reacts inside the TUI. Claude Code already has clickable overlays itself (the "Jump to bottom (click)" button), so the rendering and mouse handling is there, it's just not exposed.

What I wanted to build: a minimap of my own prompts in a long session, click one and jump there. Not possible right now, and terminal prompt marks (OSC 133) don't survive the fullscreen redraw.

What would already be enough:

• plugin-registered keybindings that run an action, e.g. scroll to a message
• read access to the rendered message list with ids
• a small overlay or side panel slot a plugin can render into, with clicks
• clickable segments in the statusline

Related, all closed by the stale bot rather than rejected: #17462, #52235, #44377. #80678 asks for the minimap natively and is about to go stale too.