feat(live-room): inline working card widget in the chat stream

[spytensor]

Closes #381.

Summary

Implements the v0.10 WorkingCard widget per the ADR (docs/v0.10-chat-stream-vs-dashboard.md) Frame B mockup. Each Working-state spawn instance now renders as a multi-line ASCII card spliced into the chat scrollback at the spawning event's chat-time position. The widget reads from SpawnInstance only — no kernel access.

┌─ @security · audit README claims ─────── working · 14s ┐
│ ✓ read README.md §2.4 security model                    │
│ ∴ cross-checking claims against src/permissions/        │
└─ 1 step done · [e]xpand [i]nterrupt [f]ocus ────────────┘

Design choices that needed picking

Card title source. The issue offered two options. I picked adding a title: String field to SpawnInstance (default empty) and wiring CrepEvent::WorkTitle through SpawnLifecycleTracker::apply_event to populate it. Rationale: the tracker is already the single ingest point for the kernel event stream, so this stays consistent with the rest of #380's model and avoids a parallel pending_titles map on the renderer. When no WorkTitle has landed yet the card top border shows the locked (no title) placeholder.

Chat position. Added a chat_position: usize field to SpawnInstance. RoomRuntimeState::apply_event stamps it via a new SpawnLifecycleTracker::set_chat_position(SpawnId, usize) setter at TurnDispatched time, using the current scrollback.len() as the splice index. This keeps the tracker renderer-agnostic — it owns the storage but never reads the value.

Splice rather than overlay. render_scrollback now builds a merged Vec<Line> that interleaves card lines into state.scrollback at each working spawn's chat_position. The existing slicing / scroll_offset / ↓ N new follow indicator (v0.9.16 #371) all continue to work because cards live INSIDE the merged scrollback rather than being rendered as a separate overlay.

Elapsed time. Rendered with Duration::as_secs() granularity. Sub-second drift cannot change the displayed string, so AC-5 (at most once per second) holds without an explicit timestamp gate.

Acceptance criteria

• AC-1: New widget WorkingCard renders one Working spawn per the visual. Reads SpawnInstance only.
• AC-2: Card sits at the spawning event's chat-time position, not pinned at the bottom. Cards scroll with history (ADR Q1).
• AC-3: Identity color from tui_style::role_color — no hard-coded literals for role identity.
• AC-4: Long tool-call summaries are middle-truncated to fit the card width.
• AC-5: Elapsed updates at whole-second granularity; sub-second drift does not change the rendered string.
• AC-6: Renderer tests cover the three required cases (see below).
• AC-7: Hotkey hint string [e]xpand [i]nterrupt [f]ocus renders but pressing the keys does nothing — v0.9.16: per-card hotkeys for working cards — [e]xpand [i]nterrupt [f]ocus #385's surface.

Validation

cargo fmt --all -- --check                  clean
cargo build --lib --quiet                   clean
cargo test --lib spawn_lifecycle --quiet    17 passed (was 14)
cargo test --lib working_card --quiet       20 passed (new module)
cargo test --lib console_room_runtime --quiet  71 passed (was 65)
cargo test --test console_terminal_qa_test --quiet  5 passed
cargo test --lib --quiet                    737 passed; 1 ignored
cargo clippy --all-targets --all-features -- -D warnings  clean

Required evidence — three rendered scenes

Scene A (AC-6a) — zero tool calls, card shows just title:

┌Room──────────────────────────────────────────────────────────────────────────────────────────────┐
│             ┌─ ◆ @security · audit README claims ── working · 0s ───────────────────────────────┐│
│             └─ 0 steps done · [e]xpand [i]nterrupt [f]ocus ─────────────────────────────────────┘│
│  @security ─────────────────────────────────────────────────────────── starting                  │
│                                                                                                  │
…
└──────────────────────────────────────────────────────────────────────────────────────────────────┘

Scene B (AC-6b) — one done + one in-progress:

┌Room──────────────────────────────────────────────────────────────────────────────────────────────┐
│             ┌─ ◆ @security · audit README claims ── working · 0s ───────────────────────────────┐│
│             │ ✓ read README.md §2.4 security model                                              ││
│             │ ∴ Grep                                                                            ││
│             └─ 1 step done · [e]xpand [i]nterrupt [f]ocus ──────────────────────────────────────┘│
│  @security ─────────────────────────────────────────────────────────── starting                  │
…

Scene C (AC-6c) — 5 tool calls (>N=3), oldest 2 dropped:

┌Room──────────────────────────────────────────────────────────────────────────────────────────────┐
│             ┌─ ◇ @backend · verify technical claims ── working · 0s ────────────────────────────┐│
│             │ ✓ step 3 of 5                                                                     ││
│             │ ✓ step 4 of 5                                                                     ││
│             │ ✓ step 5 of 5                                                                     ││
│             └─ 5 steps done · [e]xpand [i]nterrupt [f]ocus ─────────────────────────────────────┘│
│  @backend ──────────────────────────────────────────────────────────── starting                  │
…

(Scenes captured from cargo run --example against RoomRuntimeState driven through real CrepEvents — the example file itself is not committed; the equivalent test fixtures live in src/console_room_runtime.rs::tests and src/working_card.rs::tests.)

Files touched

• src/working_card.rs (new) — the widget plus 14 renderer unit tests (state gating, zero/one+/overflow tool calls, identity color, elapsed label, middle-truncation, marker glyphs).
• src/spawn_lifecycle.rs — added title and chat_position fields to SpawnInstance; routed CrepEvent::WorkTitle through apply_event; added set_chat_position setter; 3 new lifecycle tests.
• src/console_room_runtime.rs — stamped chat_position on TurnDispatched; added build_merged_scrollback; 6 new integration tests.
• src/lib.rs — registered the new module.

Out of scope (per #381)

• Hotkey wiring (#385).
• Done and Reported collapsed/report dual emission (#384).
• Footer narration (#382).
• Card density auto-collapse (#386).
• Right rail changes (#383).