feat(live-room): footer narration bar for sub-agent activity

[spytensor]

Closes #382.

Summary

Adds a one-row FooterNarration strip rendered between the body and the composer in the live room. It names the roles currently being waited on while sub-agents work, so the chat going quiet on a long delegation stops reading like the room is broken.

• The strip is hidden entirely when zero sub-agents are in Working and zero are in Spawning — the composer reclaims that row.
• The leading N roles still working count tracks only Working instances per the v0.10 ADR (docs/v0.10-chat-stream-vs-dashboard.md, "Footer narration line"). Spawning roles are named with a trailing · @role spawning chip but do not increment the count, because they have no live tool-call stream yet.
• Role chips use tui_style::role_color so colors match the @role mentions in scrollback.
• When the row would overflow, the tail truncates with … +N more. The truncation marker reserves its own space so the last chip that fits is never followed by a half-drawn chip.
• No "chat resumes when they report" wording — per ADR Q4 the line lists roles only, since v0.10 does not gate composer input on sub-agent activity.

Visuals (test-asserted strings)

Case	Rendered
Zero (hidden)	(strip not rendered — composer reclaims the row)
One Working	1 role still working · @backend
Many Working fit	2 roles still working · @security @backend
Working + Spawning	1 role still working · @security · @backend spawning
Zero Working + Spawning	0 roles still working · @qa spawning
Overflow truncated	12 roles still working · @ingestor00 … +11 more

Acceptance criteria (#382)

• AC-1: New FooterNarration strip rendered above the composer. One terminal row, no border. (render_footer_narration + conditional 5-slot layout in render_room_runtime_frame.)
• AC-2: Content derived from SpawnLifecycleTracker via working_instances_ordered_by_started_at() and spawning_instances_ordered_by_started_at(). Working drives the count + names; Spawning drives the · @x spawning suffix.
• AC-3: Role chips colored with tui_style::role_color(role, host_role). Asserted in footer_narration_chips_use_identity_colors.
• AC-4: When zero Working and zero Spawning the strip is not rendered — composer keeps its cursor row, verified by footer_narration_hidden_when_no_subagents.
• AC-5: Pluralization — 1 role still working for one Working, N roles still working (incl. 0 roles) otherwise.
• AC-6: Overflow truncates with … +N more; verified renderer never exceeds the row budget.
• AC-7: Renderer tests cover four cases — zero / one / many-fits / many-truncate — plus the locked Spawning-suffix rule and the identity-color rule.

Validation

$ cargo fmt --all -- --check         # clean
$ cargo build --lib --quiet          # clean
$ cargo test --lib console_room_runtime --quiet
running 71 tests
.......................................................................
test result: ok. 71 passed; 0 failed
$ cargo test --lib spawn_lifecycle --quiet
running 14 tests
..............
test result: ok. 14 passed; 0 failed
$ cargo test --test console_terminal_qa_test --quiet
running 5 tests
.....
test result: ok. 5 passed; 0 failed
$ cargo clippy --all-targets --all-features -- -D warnings
    Finished `dev` profile [unoptimized + debuginfo] target(s)
$ cargo test --lib --quiet
test result: ok. 721 passed; 0 failed; 1 ignored

Test plan

• cargo fmt --all -- --check
• cargo build --lib --quiet
• cargo test --lib console_room_runtime --quiet
• cargo test --lib spawn_lifecycle --quiet
• cargo test --test console_terminal_qa_test --quiet
• cargo clippy --all-targets --all-features -- -D warnings
• Full cargo test --lib --quiet (721 passing, 1 ignored)

Scope discipline

• Does not touch render_status_rail (v0.9.16: shrink right rail to scoped dashboard, move team activity out #383's surface) or scrollback rendering (v0.9.16: inline working card widget in the chat stream #381's surface).
• Does not change handle_key (no new interactions, no chip clicks/hover per v0.9.16: footer narration bar — "N roles still working" #382 out-of-scope).
• Composer height stays at Constraint::Length(5).
• Strip is one row; multi-row narration is out of scope.