feat: deliver provisional Yaoundé urban expansion dataset v2

[Omer-alt]

This PR delivers the provisional Yaoundé urban-expansion dataset v2 at 30 m resolution for 2000–2025. It replaces the former common-window Landsat logic
with exact per-epoch QA-valid window selection and rebuilds the downstream
composites, built-up candidates, states, transitions and model-ready table.

The release contains:

• 6 built-up states and 5 consecutive five-year transitions;
• 720,605 eligible cell-time rows across 210,842 unique cells;
• transition-level demand and support diagnostics;
• built area, PBA, NUMP and MPS metrics;
• schemas, data dictionary, dataset card and reproduction documentation.

NDBI is the
operational mapping method, while the generated 270-cell blind validation
sample still requires annotation.

Main changes

Landsat catalogue and composites

• Evaluates 3-, 4-, 6- and 12-month windows independently for each epoch.
• Calculates support from the exact union of QA-valid pixel masks.
• Achieves at least 95% one-observation core coverage for all six epochs.
• Adds a usable 2000 epoch and rebuilds all v2 composite/count assets.

Built-up mapping

• Exports continuous NDBI, IBI, IBUI, VbSWIR1-BI and NDBSUI diagnostics.
• Compares binary NDBI, IBUI, VbSWIR1-BI and NDBSUI candidates.
• Keeps IBI continuous-only because of unstable ratio-denominator values.
• Uses epoch-specific Otsu thresholds on valid core pixels.

Final dataset

• Applies a provisional NDBI protocol with absorbing built-state persistence on
  valid observations.
• Constructs transitions only on pairwise common-valid support and for cells
  non-built at forecast origin.
• Measures predictors at forecast origin to prevent target leakage.
• Adds final release metadata, checksums, v2 exploration and handover guidance.

Landsat support

Epoch	Selected window	Scenes	Coverage ≥1 obs.	Previously (Coverage)
2000	Mar–May, 3 months	6	98.110%	6.191%
2005	Oct–Dec, 3 months	6	95.525%	16.035%
2010	Feb–Jan, 12 months	12	98.648%	57.978%
2015	Mar–May, 3 months	16	98.079%	74.585%
2020	Dec–Feb, 3 months	12	99.888%	99.536%
2025	Nov–Jan, 3 months	19	99.888%	99.870%

All raster products use the frozen EPSG:32632 grid with 30 m cells,
946 × 1278 dimensions and transform [30, 0, 762570, 0, -30, 444150].

Reproduction and storage

The pipeline is configuration-driven and phased because Earth Engine exports
are asynchronous and five cell-time CSVs are downloaded from Google Drive.
Full instructions are in docs/reproduction_and_handover.md.

Large raw, processed and staging files remain outside Git (See on the shared Drive). Git tracks code,
configuration, compact metadata, manifests, checksums, tests and documentation.

Limitations

• Manual/AI Agent validation is pending/required; NDBI remains provisional.
• 2000 and 2005 have limited observation depth despite high spatial coverage.
• DIS, WUP and Sprawl per New Dweller are deferred.
• 1990 and 1995 are outside the active v2 scope because no usable catalogue
  products were retained under the current protocol.