Experimental Wood products C tab (HWP storage + Avoided Carbon)

[holoros]

Adds a new Wood products C detail tab and the api/hwp_storage.json data product, implementing the harvested wood products layer from issue #25.

What it does

• Per state and management scenario, charts the HWP stored-carbon pools (in-use solidwood, in-use paper, landfill, charcoal) over 2022-2122 from a WPsCS-style first-order-decay model (Wei 2022 service lives: building 80, exterior 50, home 60, paper 10 yr) driven by the PERSEUS hybrid harvest.
• A separate panel shows cumulative Avoided Carbon (substitution, DF=1.2), reported separately per the FACT (Forestry Analytics for Carbon Tracking) taxonomy and never added to stored-carbon totals.
• Self-contained HWPStorage.jsx (modeled on the Landowner-yields tab); 5-line splice into App.jsx (import, state, loader, tab, render). Does not change any existing displayed data; tab auto-disables for states without HWP data. Build verified (npm run build).

Status: experimental, review before merge

• Validated: the WPsCS-exact pool dynamics reproduce Wei's published Maine results (Building corr 1.000, Exterior 0.954, Home 0.980, Landfill 0.976).
• Key finding: at 2122 the mechanistic HWP ~ current IPCC-style layer (within ~6%), but mid-century (2050-2070) it runs ~30% lower; parameter choice dominates.
• Not finalized (do not treat as published numbers): regional product allocation (currently a national solidwood split; needs FIA TPO), and recycling (WPsCS's literal rp1+rp2*ln(yr) term is non-physical as coded — used a bounded diversion; flag for X. Wei). Coordinate reuse/citation of WPsCS before vendoring.

Closes part of #25. Methods + figures: 2026/PERSEUS/hwp_wpscs_conus_20260602/.