Add a calm "your week / month in review" summary to the Insights
overview, generated from the period-narrative context (deltas, personal
bands, FDR-controlled associations, coincident days).
- New insight_narratives table (migration 0113): one durable row per
(user, period, locale); generated prose AES-256-GCM at rest following
the coach-message precedent; labels-only provenance stays plaintext.
- generatePeriodNarrative feeds the context into the provider chain with
a tight, descriptive-never-causal prompt; an insufficient context
yields no narrative, a missing provider no-ops, neither fabricates.
- Nightly warm cron on week (Mon) / month (1st) boundaries, budget-gated
per user; the read-only GET enqueues a single-user warm on a cold read.
- Read route is stale-while-revalidate and never blocks on the provider;
the card renders plain text (no markdown), a single provenance
disclosure, and a fixed footprint (no CLS). i18n in all six locales.
