Add optional sinceYear to IAreaReference for rolling-archive append l…

[andrewcottam]

Summary

• Adds an optional sinceYear?: number field to IAreaReference (src/insights.ts), so a calculation request can say "resume from this year" instead of always recomputing full history.
• First consumer: Net Primary Productivity (ModisNPPCalculations.ts in restor2-gee-integration), prototyped and verified locally against a local AreaReferenceWithSinceYear type-augmentation cast — this PR replaces the need for that cast with the real, published field.
• Optional and additive, so this is backwards compatible for every existing caller of IAreaReference.
• dist/src/insights.d.ts is hand-updated to match the source change (rather than a full tsc rebuild, to avoid unrelated compiler-version noise across the rest of dist/). dist/src/insights.js is unchanged, since interface fields are compile-time only and emit no JS.
• Version bumped 1.9.3 → 1.9.4.

Part of the Year-Series Append Plan (rolling-archive calculations -- NDVI, Net Primary Productivity, Evapotranspiration -- appending only new years instead of recomputing history). NPP is first; this is the shared-package piece that unblocks it.

Test plan

• Verified locally against live Earth Engine (dev project, Ape Malaysia Volunteer Site 5): unfiltered request returns years 2001–2025; sinceYear: 2022 returns exactly 2022–2025, with all overlapping yValues numerically identical between the two.
• Bump restor-data-types dependency version in restor2-gee-integration once this is merged, and drop the local AreaReferenceWithSinceYear cast in favor of the real field.