fix: repair 15 rotted evidence-source URLs (batch 2) - #44

The scheduled source-health check flagged dead authoritative URLs. Each
record is re-pointed at the real underlying source and verified live.

URL/title repairs (claim unchanged, source clearly the same resource):
- landsat-lst-urban-heat-island -> USGS Landsat ST Product Guide (LSDS-1330)
- era5-land-cold-spell-analysis -> ESSD ERA5-Land reference paper
- census-migration-data-limitations -> UN DESA migrant stock (current path)
- insar-slope-deformation-monitoring -> Copernicus SentiWiki S1 mission
- icao-vaac-coverage-2024 -> ICAO Doc 9766 (Handbook on the IAVW)
- eyjafjallajokull-operational-lessons -> ICAO Doc 9974
- ioc-tsunami-warning-2024 -> UNESCO-IOC IOTWMS page
- who-uhc-2023 -> WHO item 9789240080379
- jmp-water-quality-2024 -> JMP 2023 WASH households report
- who-unicef-mhm-2023 -> JMP Menstrual Health page (was mislabeled)
- school-feeding-cost-effectiveness -> WFP State of School Feeding 2022
- who-ihr-monitoring-2024 -> WHO IHR SPAR page

Claim corrected to match the real source (old stat was unsupported):
- un-water-wastewater-2023: '80% untreated' -> UN-Water 6.3.1 '56% of
  domestic wastewater safely treated in 2022'
- unicef-breastfeeding-scorecard-2024: early-initiation 44% -> 46% (2023 ed)
- training-provider-data-fragmentation: unconfirmable 'landscape assessment'
  -> World Bank/ILO/UNESCO TVET systems report (2023), claim softened

evidence.md ledgers updated to match corrected claims.

Protocol Notes: like the FAO case in PR #42, several confident high-rated
claims carried fabricated or mismatched source titles/figures past review.
A red-team pass on high-confidence single-source numeric claims, plus a
validator linking confidence to a passing verify:sources check, would
catch this class systematically.