Add confirmed AI next-step coaching

[chudodey]

What changed

• added a validated local-AI contract for one coaching question or 1–3 physical next steps
• persisted only a compact decomposition summary and current proposal in the Markdown task
• added task-card UI to request, answer, select, and confirm proposed steps
• created child actions only after explicit confirmation and inserted confirmed steps into the fixed daily Plan
• added API tests and a sixth real-browser E2E flow
• marked CAP-003 complete and moved the backlog starting point to TREE-001

Why

Projects and problem statements are containers, not executable actions. Previously the only decomposition path required manually writing every child. The new flow lets local Ollama help identify the next reversible action without silently creating tasks or putting containers into the Plan.

Validation

• pytest -q — 131 passed, 1 skipped
• python scripts/run_e2e.py — 6 passed
• ruff check src tests e2e scripts main.py
• node --check web/static/app.js
• python scripts/backlog.py --check
• live qwen3:4b check: one question on the first turn, three concrete steps after a synthetic answer