fix(ingest): preserve valid RFC3339 packet timestamps

[n30nex]

Valid whole-second, millisecond and nanosecond packet timestamps with numeric UTC offsets could be replaced by receive time. Use Go's RFC3339 parser plus the existing timezone-less UTC fallback. Preserve malformed-input fallback and the 30-minute skew clamp; no schema, API or dependency change.

Closes #181. Independent on accepted dev. The ingest regression failed first and now covers Z/+00:00/-04:00/+05:30, four precisions, legacy timezone-less input and invalid/future/stale timestamps. The live one-minute sample had zero parser fallbacks; skew and malformed-IATA warnings remain.

Parent db30c9b573357990c41166292e7cf42785c92cc4, head c39df3043931dbe37d51a73d15f050a1c61d1a3b. Focused diff.

Published-head CI and the complete combined native Pi/PostgreSQL suite pass. The Pi runs server a35cba1d / web e1133ab5, retaining every review candidate. Windows/Pi web build/lint and all 940 tests pass. The isolated 3,200-input/504-scope replay preserved expected data/events with zero fixture drops; this is not a universal production losslessness claim. Validation, exact heads and recovery / running source.

Maintainers retain merge/release control; AI-assisted work continues under the contributor's standing authorization.

[n30nex]

@MrAlders0n / Claude: addressed at c39df304.

Ready for review: this fixes #181 without changing delivery/deduplication or the skew policy. The failing-format reproduction, full local/native suites and exact-head CI pass. The candidate is included on the Pi preview.

Published-head CI and the complete combined native Pi/PostgreSQL suite pass. The Pi runs server a35cba1d / web e1133ab5, retaining every review candidate. Windows/Pi web build/lint and all 940 tests pass. The isolated 3,200-input/504-scope replay preserved expected data/events with zero fixture drops; this is not a universal production losslessness claim. Validation, exact heads and recovery / running source.

Please take another look when convenient; no upstream merges were performed.