Modernize composer and interaction surfaces

[dovvnloading]

Summary

This PR consolidates the recent local UI and interaction-surface repairs into a production-oriented update.

Composer and context UX

• Keeps the composer fixed to the application surface instead of treating it as a graph element.
• Removes the noisy context title bar, node-title duplication, token summary, and inline React context review surface.
• Adds a stable paperclip attachment action with an explicit-attachment count badge.
• Delegates detailed context review to the native, viewport-aware popup so it is not clipped by QWebEngine.
• Clears submitted composer text immediately while preserving recoverability on failure/cancel.
• Adds native model and reasoning selectors with stable sizing and top-level z-order.

Interaction and menu surfaces

• Hardens context-menu rendering and ownership.
• Adds native popup positioning, masking, scrolling, and removal behavior for composer context and selectors.
• Updates graph/node interaction paths and utility menu behavior to use consistent native surfaces.

Model/settings and supporting behavior

• Improves model discovery and selection state handling across local and cloud routes.
• Preserves the send contract and bridge compatibility while making UI state updates deterministic.
• Includes chart/node and context-data handling cleanups plus regression coverage.

Validation

• npm.cmd run check — TypeScript typecheck and production Vite build
• 35 focused Python regression tests passed
• Python compilation passed for composer, bridge, popup, window, and action modules
• git diff --check passed

The local-only Doc folder is not part of this commit.