feat(demo-got): add Game of Thrones family tree HelixDB demo

[kevinmichaelchen]

Summary

• Add new demo-got crate demonstrating HelixDB graph capabilities
• Uses Game of Thrones family relationships (30 characters, 88 edges)
• CLI with ingest and query commands
• Showcases graph traversal (ancestors, descendants, house members)

Features

# Ingest family tree into HelixDB
cargo run -p demo-got -- ingest

# Query Jon Snow's ancestors (reveals R+L=J!)
cargo run -p demo-got -- query ancestors jon-snow

# Query Ned Stark's descendants  
cargo run -p demo-got -- query descendants ned-stark

# Query House Stark members
cargo run -p demo-got -- query house stark

# Get person details with family
cargo run -p demo-got -- query person ned-stark

# JSON output
cargo run -p demo-got -- --json query ancestors jon-snow

Test plan

• cargo fmt --check passes
• cargo clippy -D warnings passes
• cargo test -p demo-got passes (2 tests)
• cargo run -p demo-got -- ingest creates database with 30 nodes, 88 edges
• cargo run -p demo-got -- query ancestors jon-snow shows correct lineage
• Database persists across process restarts