Add openmined.org affiliation logos to OMDS (logos/orgs/) (#15)

Systematically pull the third-party logos used on openmined.org into a new
affiliations namespace — distinct from the tool partner set:
- 18 orgs (Microsoft, Meta, Reddit, X, PyTorch, NIST, AISI, Census, Royal
  Society, SSIR, TPG, UK DSIT, NTIA, White House, UN Big Data, US Senate,
  NSF, Executive Office). Sourced from OM's existing site SVGs (cleaned),
  + official Wikimedia vectors for NSF + Executive Office (OM's were raster).
- color + token-aware 1-color (currentColor) for the 13 clean marks;
  detailed multi-color seals are color-only (no clean 1-color).
- orgs.json manifest (owner, category, usage-restricted flag for gov seals,
  provenance, gaps); "Affiliations" styleguide section reads it.
- Governance: third-party trademarks, nominative use, never recolored; gov
  seals flagged usage-restricted. Google/Anthropic stay in the tool set.
- Gap: Christchurch Call has no public vector (JPG only) — documented.

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: bennettfarkas