The Settings → Dashboard sub-section's Save button silently 422'd once
the user had touched any per-chart overlay popover. Root cause was a
Zod v4 semantics change: `z.record(z.enum(KEYS), ...)` now requires
every enum key to be present in the input, where Zod v3 treated the
same shape as a partial record. Real-world Save payloads only carry
the chart keys the user actually toggled, so every Settings → Dashboard
Save attempt with one or two `chartOverlayPrefs` entries failed with
`expected: object, path: ["chartOverlayPrefs", "<missing-key>"]` and
the toast surfaced "Layout konnte nicht gespeichert werden".
Fix uses `z.partialRecord(z.enum(KEYS), ...)` which preserves the
original v1.4.18 intent — per-chart opt-in overlay prefs, missing keys
filled by the resolver. The inner object now also accepts the
`comparisonBaseline` field so a Settings save preserves the per-chart
comparison toggle the user set via the chart-card popover (otherwise
Zod's default strip behaviour wiped it on every save).
New integration suite pins:
- partial chartOverlayPrefs round-trips
- per-chart comparisonBaseline survives a Settings save
- empty chartOverlayPrefs still persists (fresh accounts)
- widget toggle changes land in the DB
