Expand bestiary with new creature families, corruption archive, and regional ecosystem indexing

[Copilot]

This update expands the bestiary from a flat entry list into a more navigable field guide by adding family-level grouping, threat-tier organization, and regional ecosystem mapping. It also adds the requested missing creature sets (corruption/undead/reactor, goblin-orc, ancient desert, nature/swamp, constructs/giants, humanoid factions, and wildlife) while preserving the one-primary-entry-per-species model with variants kept in-subsection.

• Bestiary information architecture

  • Added Creature Family Groups for quick taxonomy-level browsing.
  • Added Creature Threat Tiers for encounter planning (Ambient Wildlife → World Bosses).
  • Added Expanded Regional Ecosystems to map species to island ecology and improve island-to-creature traversal.

• New creature coverage (requested groups)

  • Added new primary entries for the missing requested species across:
    • corruption / undead / reactor entities
    • goblin and orc groups
    • ancient Sunscar dynasty creatures
    • forest/swamp nature creatures
    • golems/giants/constructs
    • humanoid enemy factions
    • fish and shark wildlife
  • All new entries follow the canonical section schema and include ### Variants (no separate variant pages created).

• Cross-link and naming consistency

  • Added anchor-linked references across family groups, regional ecosystems, and entries.
  • Resolved habitat-to-region mismatches in expanded ecosystem lists for newly added entries to keep placement and entry metadata aligned.
  • Normalized newly added threat labels to the existing document pattern (Low | Medium | High | Boss).

• Representative snippet

  ## Creature Family Groups
  
  - **Corruption Legions**: [Demon Skeleton](#creature-demon-skeleton), [Skeleton Knight](#creature-skeleton-knight), ...
  - **Sunscar Dynasties**: [Ancient Queen](#creature-ancient-queen), [Ancient Warrior](#creature-ancient-warrior), ...
  
  ## Expanded Regional Ecosystems
  
  ### [Veilreach Isle](islands.md#veilreach-isle)
  - [Demon Skeleton](#creature-demon-skeleton), [Plague Undead](#creature-plague-undead), [Necromancer](#creature-necromancer), ...