[C5] Complete bounded-parallel task dispatch and retries

[ACFHarbinger]

Continue the C5 workflow implementation.

Current state in commit a2ef8ed:

• sequential task dispatch is available;
• task schema persists retry counters, parallel-stage queues, pending agents, and max_parallel;
• desktop and CLI task surfaces remain sequential.

Next work:

• implement bounded parallel dispatch and queue release;
• add retry command/behavior honoring WorkflowStep max_retries;
• persist failed terminal state and emit handoff/wake audit records;
• add CLI/Tauri tests and update the C5 roadmap when complete.

[ACFHarbinger]

C5 is now implemented in ce63a24 and documented in 0c13bc3. Workflows support sequential and bounded-parallel stages, queued-agent release via task complete, per-stage retry limits with failed terminal state, and CLI/Tauri surfaces. cargo test --workspace and npm run build pass. Remaining roadmap work is C6 budget-aware pause/delegation and C8 fully parallel session startup.