[Writer] Remove Lumia chain and add deprecation notice

[JackReacher0807]

Changes

• Deleted Lumia API pages (quickstart, FAQ, overview)
• Created Lumia deprecation notice page (modeled after Fantom's)
• Removed Lumia from node-supported-chains card grid and RPC endpoints table
• Removed Lumia from alchemy-sandbox supported chains list
• Deleted Lumia OpenRPC spec and generator config
• Updated docs.yml nav to show only deprecation notice
• Added redirects: /docs/reference/lumia-api-quickstart, /docs/reference/lumia-api-faq, /reference/lumia-api-endpoints → deprecation notice
• Updated dynamic redirects: /docs/node/lumia/* and /docs/chains/lumia/* → deprecation notice

Closes Asana task 1213209038903047

[github-actions]

🌿 Documentation Preview

Name	Status	Preview	Updated (UTC)
Alchemy Docs	✅ Ready	🔗 Visit Preview	Feb 10, 2026, 1:49 AM

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