feat(api,docs): e2e demo pipeline + showcase script

[w7-mgfcode]

Summary

Close the demonstrability gap surfaced in INITIAL-14.md and detailed in PRPs/PRP-15-e2e-demo-pipeline.md: examples/e2e_smoke.sh only asserts /health, and Phase-2 seeder/featureset work (PRs #111/#112/#114/#115/#127) has no scripted exit channel. Land a single make demo command that drives the published HTTP surface end-to-end in ≤ 180 s on a developer laptop.

Scope (additive only)

• New scripts/run_demo.py — async, httpx-driven, RFC-7807-aware; walks seed → status → features → train ×3 → backtest → register → alias → verify → agent-roundtrip.
• New top-level Makefile with demo, demo-quick, demo-clean targets.
• New seeder preset (demo_minimal or pinned retail_standard subset — see PRP Open Question Q1).
• Unit tests: tests/test_run_demo_unit.py.
• Integration test: tests/test_e2e_demo.py marked @pytest.mark.integration.
• Doc updates: README.md, docs/DAILY-FLOW.md, docs/_base/REPO_MAP_INDEX.md, docs/_base/RUNBOOKS.md.
• Opt-in .github/workflows/e2e-nightly.yml — cron + workflow_dispatch, not PR-blocking.

Non-goals

• No schema changes, no Alembic migrations, no API edits.
• No Phase-2-aware LightGBM training (queued as PRP-16).
• No dashboard "Run demo" button (follow-up).

Acceptance Criteria

• make demo exits 0 on a fresh docker compose up -d && uv run alembic upgrade head host.
• Wall-clock ≤ 180 s on the reference laptop (soft-warn above; no fail).
• Final line: runs=3 winner=<model_type> alias=demo-production wall_clock=<t>s.
• GET /registry/aliases/demo-production returns the winning run_id.
• GET /registry/runs/{winning_run_id}/verify returns verified=true.
• Agent step round-trips successfully or is skipped with ⏭️ [SKIP] when no LLM key is set.
• tests/test_run_demo_unit.py and tests/test_e2e_demo.py (integration) pass.
• ruff check + ruff format --check + mypy --strict app/ + pyright app/ clean.

References

• INITIAL: INITIAL-14.md
• PRP: PRPs/PRP-15-e2e-demo-pipeline.md
• Vision alignment: .claude/rules/product-vision.md § Core Principle 1, § Litmus Test sync: merge main into phase-0 #5
• Output formatting: .claude/rules/output-formatting.md

[w7-mgfcode]

Resolved by #129 (merged to main). Closing — fix is shipped.