[urgent] restore ClaudexHub branding everywhere

[junseo2323]

What changed

• Restored the product brand to ClaudexHub across the UI, docs, API metadata, logs, instructions, and deployment configuration.
• Renamed the npm package and executables to claudexhub / claudexhub-cli at version 0.3.0.
• Renamed the MCP registration to claudexhub, token prefix to clx_, and public environment/config identifiers.
• Added migration cleanup for legacy context-hub agent registrations and compatibility reads for existing session/config values.

Validation

• npm run typecheck
• EMBEDDING_PROVIDER=noop npm test — 105 tests passed
• npm run build
• npm run web:build
• Installed the packed claudexhub@0.3.0 tarball and verified its CLI.
• Rendered the landing page and confirmed no legacy product-brand text remains.