Add TNFD/CSRD skill suite

[alexlogs]

Five new skills for nature-related and climate disclosures, all built on top of subscribe-and-load and compute-area-by-threshold:

• screen-portfolio: foundation for any multi-AOI workflow.
• deforestation-risk-screen: Hansen forest-loss screen for TNFD Locate and CSRD E4 (without the EUDR-specific cutoff).
• land-cover-baseline-and-change: per-class composition and deltas for CSRD E4 ecosystem extent and TNFD Evaluate.
• priority-biome-overlap: TNFD Locate sensitive-locations check using forest-type / biome rasters.
• land-use-carbon-flux: screening estimate of land-use emissions for CSRD E1, combining land-cover transitions with carbon density.

What this adds

Checklist

• Right folder (tutorials/, use-cases/, or skills/) — see CONTRIBUTING.md
• Notebook: validates with nbformat, runs end-to-end against the live SDK, title cell at top
• Skill: frontmatter has name, description, license: MIT; directory name matches name
• No secrets (API keys, account IDs) committed
• AOI/example is modest in size if applicable