v0.9.16: footer narration bar — "N roles still working"

[spytensor]

Context

Per umbrella #377 and ADR #378, when @host has delegated and is waiting on sub-agent reports, the main chat goes silent in a way that today reads as "the room is broken." The footer narration line explains why and lists who is being waited on.

Required Visual

A single line, rendered between the chat stream and the composer:

2 roles still working · @security @backend · chat resumes when they report

When nothing is in flight: the line is hidden (do not render an empty bar that would steal a row).

Acceptance Criteria

• AC-1: A new FooterNarration strip is rendered above the composer. It uses one terminal row, no border.
• AC-2: Content is derived from the lifecycle records from #380: list of roles currently in Working state.
• AC-3: Role names use their identity colors (same color module as @role mentions in scrollback).
• AC-4: When zero roles are Working, the strip is not rendered — the composer gains that row back.
• AC-5: Pluralization is correct (1 role still working vs N roles still working).
• AC-6: If more roles are working than the row can fit, role chips truncate with … +N more.
• AC-7: Renderer tests cover the four cases: zero / one / many-fits / many-truncate.

Note on the "chat resumes when they report" wording

The phrase asserts a behavior (chat input is queued or paused while sub-agents work). If the production room does not behave this way today, the wording must be adjusted to describe actual behavior, not aspirational behavior. Decide during implementation; do not promise behavior we do not ship.

Out of Scope

• Changing whether / how chat input is gated during sub-agent work.
• Click / hover interactions on role chips.
• Showing tool-level detail in the strip (that lives in the cards).

Required Evidence

• Renderer tests above.
• Two screenshots: zero roles working (strip hidden), two roles working (strip shown).