Stabilize conversation card presentation

[VolkerChristian]

Summary

• retain an admitted prompt card through authoritative acknowledgement and promote it to canonical user styling in place
• reserve canonical border geometry for pending prompts and show newly inserted cards before synchronous layout measurement
• keep Agents inspector status and path metadata visible without the empty vertical band

Why

Resolved prompt cleanup previously discarded the local visual identity, so acknowledgement removed and recreated the You card. Newly inserted child cards also remained implicitly hidden during the reconciliation measurement and received their final geometry only in a later Qt layout pass. This caused visible movement, especially with a paused viewport and an expanded command card.

The card-kind audit confirmed that first appearance affected every rendered kind; same-kind lifecycle updates were already stable.

Regression coverage

• prompt cleanup retains the compact authoritative-to-local visual alias
• acknowledgement preserves the exact ConversationCard widget, folded state, canonical kind/style, and stopped animation timer
• pending and canonical prompt states use identical frame geometry
• every card kind arrives at its settled height while a paused, expanded completed command retains its position, height, painted geometry, anchor, and inner-output scroll state
• Agents metadata labels retain visible geometry in a realistic wrapped two-agent layout

Validation

• full CMake build succeeds
• 7/7 CTest suites pass
• live prompt acknowledgement test: no remove/reinsert flicker
• two live runs of ten command cards at one-second intervals while paused with an expanded command visible: no flicker
• Agents spacing verified in the installed combined build