API timestamps emitted in UTC, not the user's local zone — violates timezone contract #13

internal/cronoclient/client.go hard-codes time.UTC when calling the gocronometer parsers:

recs, err := c.inner.ExportServingsParsedWithLocation(ctx, rng.Start, rng.End, time.UTC)         // L42
recs, err := c.inner.ExportExercisesParsedWithLocation(ctx, rng.Start, rng.End, time.UTC)        // L51
recs, err := c.inner.ExportBiometricRecordsParsedWithLocation(ctx, rng.Start, rng.End, time.UTC) // L60

This produces JSON timestamps like "RecordedTime": "2026-04-24T00:00:00Z" regardless of the host zone, e.g.:

$ /tmp/crono-export servings --since 7d --format json | jq '.[].RecordedTime' | sort -u
"2026-04-18T00:00:00Z"
"2026-04-19T00:00:00Z"
...
"2026-04-25T00:00:00Z"

Per the quantcli timezone policy: API timestamps should be .Local()-ed before bucketing/formatting, and JSON should keep the RFC3339 offset (e.g. 2026-04-24T00:00:00-04:00). The downstream markdown date-bucketing in cmd/format.go (r.RecordedTime.Format(\"2006-01-02\")) also assumes the timestamp is in local zone, so on machines west of UTC a record logged at 9pm local on day N currently buckets one day late.

Fix: pass time.Local instead of time.UTC to the three ExportXxxParsedWithLocation calls.

Severity: major