tune(bot): medium spread 20%->30%

feat(bot): weaker bots sometimes pick another plausible option (spread by level)

feat(bot): difficulty cuts whole LOCATIONS not frames (frac = fraction of known panos)

feat(bot): dynamic ?frac= index density (server-computed via admin config); drop hardcoded tier %

feat(bot): dynamic Easy/Medium tiers for ALL region models (seeded 5%/25% row subsample by skill)

chore(health): report region easy/medium tier sizes

feat(bot): Germany Easy/Medium difficulty tiers via skill-selected sub-indexes

feat: add 107 country region models + graceful skip on missing index

Move region indexes to HF dataset (geobot-indexes); load on demand via hf_hub_download