docs: cleanup chain navigation, remove stale tools and refactor flashblocks content

[roethke]

What changed? Why?
Removes the "Tools" section from Base Chain and redistributes its pages to more logical homes. Fixes a docs.json validation error, and regenerates LLM index files.

• Node Providers → Node Operators
• Network Faucets → Network Information
• Block Explorers + Data Indexers → new "Developer Tools" group in Get Started
• Renamed apps.mdx → app-integration.mdx; added redirects from old URLs
• Deleted 8 stale tool pages with redirects (Base Products, Onchain Registry, Oracles, Onboarding, Cross Chain, Account Abstraction, Onramps, Tokens in Wallet)
• Renamed flashblocks/node-providers.mdx → run-a-flashblocks-node.mdx to disambiguate from the Node Operators "Node Providers" page
• Merged websocket-reference.mdx into api-reference.mdx; added redirect, removed outdated content
• Replaced stale method-link table in run-a-base-node.mdx with a single link to the Flashblocks API Reference; added link to Infrastructure Stream schema from the WebSocket Endpoints note
• Fixed invalid "assistant" contextual enum causing Mintlify validation error (breaking mint dev)
• Fixed Etherscan link, incorrectly pointed to Basescan: source
• Fixed stale links in node-providers.mdx and LLM index files (flashblocks/docs → flashblocks/faq)
• Regenerated relevant LLM files

Notes to reviewers

How has it been tested?
Locally

[cb-heimdall]

✅ Heimdall Review Status

Requirement	Status	More Info
Reviews	✅ 1/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1