v0.2.8 — Real DB error visible in chat banner

Patch on top of v0.2.7.

What

The chat-error banner introduced in 0.2.7 surfaced `error.message` as-is. Drizzle wraps every postgres failure with a `Failed query: params: ` template at the top of the chain — the actual postgres reason (the part you need to fix) sits invisible inside `error.cause`. Visible symptom: pages of 768-dim vector dumps, no actual reason named.

Fix

New `` walks the cause chain and surfaces the first non-wrapper message as the headline — that's the postgres reason in nearly every drizzle case ("operator does not exist", "relation does not exist", "vector dimension mismatch", etc.). The SQL + outer wrappers tuck into a collapsible "Technical details" section so they're available when needed but don't dominate the page.

Hint copy nudged to also mention Settings → Models, since most of these errors are embed-model / chunk-model mismatches after the user changes embedding selection without re-embedding.

What you'll see

Re-trigger the failing chat — the banner will now show something like:

operator does not exist: vector <=> vector
If this persists, open Settings → Providers and re-test the chat provider, or Settings → Models to confirm the embedding model matches the chunks already stored.
▶ Technical details

Commits

```
b1338e0 fix(chat): walk error.cause chain to surface real DB error — bump 0.2.8
```

Full diff: v0.2.7...v0.2.8