feat: add Mintlify documentation site

[TinDang97]

Summary

• Set up a complete Mintlify docs site in docs/ with maple theme and indigo color scheme
• Created 10 documentation pages covering all major areas: quickstart, architecture, configuration, command reference, benchmarks, and guides for persistence, clustering, TLS, and Docker
• Generated logo (light/dark) and favicon assets via Gemini image generation

Pages

Page	Description
index.mdx	Landing page with key metrics and feature cards
quickstart.mdx	Build from source, Docker, client library examples
architecture.mdx	Thread-per-core design, DashTable, memory layout
commands.mdx	All 200+ supported commands by data type
configuration.mdx	All CLI flags with production example
benchmarks.mdx	Full performance data with reproduction steps
guides/persistence.mdx	AOF, RDB, per-shard WAL
guides/clustering.mdx	Replication, cluster mode, failover
guides/tls.mdx	TLS 1.3, mTLS setup
guides/docker.mdx	Container deployment patterns

Test plan

• Run cd docs && mint dev with Node 22 and verify all pages render
• Verify navigation structure matches docs.json
• Check internal links resolve correctly (mint broken-links)
• Verify logos and favicon display in light/dark modes