Fail-closed startup, view cache, and 503-until-refreshed serving path (FIX-14)

[ChelseaKR]

app/server.py::_load_view re-resolved config, opened the store, and could run
a full first-run ingest inside a request; every request rebuilt
stats/wrapped/diversity/recommendations with no caching, and pyproject.toml
still omitted app/server.py from the coverage gate despite existing
TestClient tests.

• Add a FastAPI lifespan (_lifespan) that resolves config and probes the
  store once at startup, failing closed like app.auth.AuthNotConfigured:
  raises ConfigInvalid on bad config, StoreUnavailable on an unreachable
  store. A never-refreshed store only logs a warning — it does not block
  startup.
• Cache the built DashboardView on app.state, keyed by
  (store_path, refreshed_at stamp, hash of view-relevant config fields) via
  a new Config.view_cache_fields() helper; a request only rebuilds the view
  when the store was actually refreshed or the config actually changed.
• Remove the inline first-run ingest from _load_view; data routes (/,
  /browse, /share, /share/card.svg) now return 503 until an explicit
  stacks refresh populates the store. No route runs ingest inline.
• Remove app/server.py from pyproject.toml's coverage omit list (the

  =85% --cov-fail-under gate is unchanged); app/server.py now measures at
  98% coverage.

• Add tests/test_server_lifecycle.py covering populated-store routes, the
  503 path, cache reuse/invalidation across a refreshed_at bump, and
  lifespan failing closed on bad config/store. Update test_auth.py,
  test_goals_time.py, and test_observability.py (via a new
  tests/conftest.py::seed_store_from_env helper) to seed the store
  explicitly before hitting data routes, since ingest no longer happens
  inside a request.
• Mark FIX-14 done in docs/ideation/02-large-scale-fixes.md.

Full suite: 206 passed, 96.6% total coverage. make lint/typecheck/test all
green.

Co-Authored-By: Claude Fable 5 noreply@anthropic.com

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Backfill PR for a completed roadmap item (roadmap/fix-14-serving-path-lifecycle-startup-ch, 1 commit(s) over main). Part of the portfolio roadmap batch.