feat: improve mobile conversation experience

[wisdomqin]

Summary

• lighten mobile Thinking and tool-call rows, render ask-user-question interactions, and surface Todo projections
• add mobile model and Preset settings with first-message Preset locking, plus optimistic user-message rendering
• polish the composer and empty-session flow, and pin the running “Deep diving...” state directly above the composer instead of inside the scrolling message list
• expose the required mobile RPC adapters for pending interactions, model selection, Preset selection, and projection data

Verification

• npm run typecheck
• npm test -- --run (27 files, 170 tests)
• npm run build

The desktop app was intentionally left stopped after verification.

[wisdomqin]

Fixed the missing mobile ask_user_question delivery path. The real network Harness serves /api/events.mux as a downlink-only WebSocket and returns HTTP 426 to ordinary GET requests; the bridge had incorrectly implemented that stream as SSE. The regression fixture now mirrors the production WebSocket upgrade and verifies replay, answer, resolution, cancellation, and validation.

[wisdomqin]

Fixed the settings popover jumping upward when Todo and running-status docks are present. The popover now remains anchored 76px above the composer trigger; Todo expansion and Deep diving... only affect message clearance, not popover placement. Typecheck, all 170 tests, and the production build pass.

[wisdomqin]

Restored the original mobile Deep diving... behavior after product review: it is again rendered as the final item in the scrolling message flow, rather than a fixed composer dock. The Todo/settings positioning and WebSocket question-delivery fixes remain unchanged. Typecheck, all 170 tests, and the production build pass.

[wisdomqin]

Removed the stray native file-picker control from the Agent presets header. The hidden input remains as the backing control for the styled Import button, and the patch now explicitly applies display:none. Patch reverse-check, typecheck, all 170 tests, and the production build pass.