Refactor truth surface into shared receipt and projection helpers

[Hmbown]

Scope

Refactor the truth surface so sidebar/footer/activity detail do not each invent their own view of command/tool/session state.

Acceptance

• Introduce or extract a shared receipt/projection layer for active command/tool/subagent state.
• Sidebar cockpit rows, footer live chips, and Activity Detail consume the same source data.
• Budget rows reuse existing token/cost/currency helpers; no hardcoded USD or message-count token estimates.
• Tests cover one source of truth feeding multiple projections.

Starting smell

The v0.8.41 cockpit patch duplicated context/cost/tool status in tui/sidebar.rs. This milestone should eliminate that pattern.