feat(insights): a date on each conclusion, and no category enum

[mrviduus]

Acting on the consilium's one unresolved question, which the owner answered: the return path is per-book ("I open Dracula and see what I worked out about it"), and one insight per chapter, refined over time.

Both answers remove work rather than adding it.

The category enum is not being built

Per-book retrieval is served by a chapter label and reading order — both already ship. Tabs over ≤10 insights are an empty-state generator, and a category in the unique key would take the write ceiling from 1 × chapters to 4 × chapters while falsifying the replace promise the tool description makes. Revisit only if retrieval ever turns cross-book ("every open question across all 33 books"), which is the one shape that genuinely needs a typed field — and which would also need the filter-less /me/insights route that answers 400 today.

What the panel was actually missing is a date

A конспект is read months later. Without a date it cannot answer "is this what I thought then, or what I think now". A re-run replaces the row and moves updatedAt, so this is the age of the current text, not of the conversation that started it.

• Absolute, not relative. "3 days ago" is the right register for a shelf of things in progress and the wrong one here; by the time this matters the answer is months.
• ISO, because the shared package holds no locale, and because a local calendar day would show the same insight under two different dates on two devices — which the test pins with a +03:00 timestamp that is still the previous day in UTC.
• Null on an unparseable timestamp, so a bad row loses its date rather than printing Invalid Date beside a conclusion.

One pure function in shared, rendered by both clients. No schema change.

Verification

• shared 452 (3 new), web 711, mobile 369 — pass
• tsc --noEmit web + mobile — clean

🤖 Generated with Claude Code

https://claude.ai/code/session_011rgEMvYYi4Egj99dVtvm6E